I know this may sound harsh but If they like hiking, walking and biking, this is not the itinerary that will give them that. A week on the Amalfi coast, followed by a few days in each of Rome and Venice, then a week in the Dolomites, a few days on one of the italian lakes, a few days in Milan, then train to Interlaken and spend a week in the Berner Oberland - that just about fills their 5 weeks and seems much more tailored to their interests.

Hiking and biking.....

The PO valley is famous for its cycling.

Hike in Austria or Southern Germany.

Too Much
 

That would be a great itinerary for a college student with unlimited energy who want's to 'tick the boxes'. I'm not going to create an itinerary for you b/c you need to do that. With that said, a few thoughts:

• Rome is easily worth a full 4 days, Florence 3, Venice 2-3. To simplify, I would prioritize your list of cities and drop the bottom third. For all I know, your parents have relatives in Milan, Bern, and Naples, if they don't, I'd rank those places farther down the list to refine and focus the itinerary.
• Salzburg is great (we were there for Christmas!!), but relatively speaking, more time in Vienna than Salzburg.
• Consider researching side trips out of the main cities, e.g. Ostia Antica near Rome, Pompeii near Naples, the concentration camp near Munich, Neuschwanstein near Munich, bike tours in Tuscany outside Florence, Cinque Terre and Pisa near Florence, the islands of Burano and Murano by Venice, etc. etc. That will enrich their trip and keep them from moving around so much.
• Also consider that after walking around city streets for 6-7 days and visiting innumerous cathedrals, palaces, and museums, some down time is in order. For example, on one of our trips, we started with Venice for a few days, then Florence for 4 days, then Pompeii, and then we went to Sorrento and the Amalfi Coast for some R&R before starting up once again for 5 days in Rome. It's a great way to recharge one's batteries and enjoy life.
• Perhaps consider a Eurorail pass of some type. Trains are a great way to see Europe, are relatively timely, and notably more relaxing than airlines.
• You did not mention if they might consider another trip perhaps next year. If so, you might consider parsing off the eastern end of the trip and creating a separate trip of Berlin, Prague, Vienna, Bratislava, Budapest, and maybe even Croatia (e.g. Split) which is absolutely fantastic these days. If so, this would also help refine and focus the trip at hand.
• Watch a Rick Steve's Youtube video ( or comparable Top 10 things to see) on each and every one of your proposed destinations - that's an order. It's also a gift b/c you get to take a mini-virtual vaca and learn about the proposed destinations to help you make a more informed set of decisions.

If it was me, I'd do the following:

1. Venice - 3 days including either Murano or Burano)
2. Florence - 3-4 days including one day in Pisa. Also research Cinque Terra which is is fanciful, great hiking, on the coast, but probably adds an extra day.
3. Amalfi Coast - 3 days (include Pompeii with that either on the way to or the way from), and we agree with others above that Sorrento is a very nice place
4. Rome - 5 days with a day trip such as Ostia Antica (there are other side trips as well)
5. Spend 4-5 days in Switzerland and do day trips. Get some R&R in the mountains, hike in the mountains, go hang gliding, Have fun in the fresh air! Interlaken is a nice location.
6. Munich for 4 days including the concentration camp and Neuschwanstein. HOWEVER, if they are in Munich in September, beware that Oktoberfest is then so the place will be crowded and crazy!
7. Salzburg for 2, Vienna for 3-4 days
8. Lisbon for 2

That's a total of 32 days and if you add a 1/2 day of travel between each location, that pretty much adds up to around 35 days or 5 weeks. Even that itinerary is too busy - but eminently more reasonable and doable than the original proposal. I would hold off on Prague and Berlin and add those to a future trip as noted. They are both good for 4 days plus travel time which means you would need to do some extreme surgery on the rest of the itinerary.

Let us know what you ultimately decide on!!! Anyway, I hope this helps.

D.

I maintain an old website that offers advice on European cycle holidays for the older person


Mybikeguide.co.uk

Let them have a look

60 is not elderly

The stated desires: 2 active adults who like hiking, biking, and walking but are apprehensive about getting around/not understanding the language (s).
And proposed plan: 5 different countries (that's 3-4 different languages), focused on cities (none of which are good for hiking or biking).

Those 2 things don't jive.... It's like saying "we don't want greasy, fast food" then planning a dinner date at McDonalds the being surprised at what you get. Perhaps start with what they do like, then look for places that focus on the desires.

Southern germany and salzburg area are great for hiking - consider basing somewhere like Garmish Partenkirchen (GP) for a week. On a family trip many years ago I used that as a base for an entire month and it was one of my favorite trips.
The low countries - Belgium, Netherlands, and even northern France are wonderful for biking. I've done bike trips there over several days all on bike trails and it's one of the best trips I've ever done.

I have planned and executed some pretty energetic itineraries (New Zealand in 9 nights, for example.)

That said, I always leave some of every 4th day open for stuff like taking care of laundry, adjusting train reservations, catching up (trains can be late especially if there is a 1 day strike, which can happen a lot in Italy.)

Speaking of trains, that trip from Bern to Salzburg is over 6 hours, and involves a change. Try to work things so that you have only 3 hours of travel max in one segment. That way you never fall too far behind if for some reason a journey gets delayed. Google is your friend, just type 'train A to B' and you'll get an approximate idea of schedules (fine tune as seasonal schedule becomes available.) Of course sometimes breaking the trip is awkward to do but in that case just bear in mind that after a long train journey you won't want to tear around the next day.

Next: hiking in Switzerland is lovely but you might need to plan for the odd rainy day. It would be just too much to have to leave the Lauterbrunnen Valley in the sunshine after your sole full day planned there turned out to be rainy or foggy. Forget Jungfraujoch, it is expensive and you would end up breezing past places like Kleine Sheidegg where hiking is lovely. Or consider other posters' suggestions for hiking. Just remember you may need some ideas for what to do if the weather is not hiking friendly.

I also picked up right away that you are trying to help them refine their original plan, one that was a bit nuts in places. Bless you.

FYI--we are truly geriatric (66 and 75), and my husband doesn't speak one word of any other language. My husband likes to walk, walk, walk, walk. I could camp out for hours with my Kindle on a window seat in some European apartment with a view and be just fine. Yet like bilboburgler, we were cyclists and have only just recently given up our bike tours of Europe, New Zealand, etc. We rely on public transport--trains, buses and taxis--everywhere and are quite happy with that style of travel. We love seeing art and we love hanging out meeting locals. In other words, I don't think we are that much different from your parents, except my husband doesn't have five straight weeks because he insists on working after 75 (boo, hiss).

Anyway, first, congrats to them that they are not taking a cruise--large ship or river.

Bilboburgler has already expressed what I was thinking. They need laundry stops and downtime so that they can energize themselves for all the "uppy.". And that's the point I'd emphasize to them. Even though our overseas trips are a best three-week things now, we know we do best with a minimum of 3 nights. Yes, we've had to schedule a one-nighter here or there and also have to deal with 2-nights within our 3-week travel, but 3- or 4-night stays help us fit in all the drudgery (laundry, temperature-reorganization of luggage, etc) of travel. I really never feel the need to go back home when we've spaced things this way because each stop becomes our home. Also, our "memory banks" of each place become truly full.

We've been to every single place on their original trek except for Salzburg. Anyway, I've given thought to their Switzerland leg, and I hope they do it. This is my input IF they account for the unbelievable COST of Switzerland (we think the Swiss provide value, though): I'd use Wengen as a base. That could give them the wiggle room they need for weather-dependent hiking. We loved Bern (one of the most underrated cities in all of Europe) and valued Interlaken as a transport hub, but we think centering oneself in Wengen would still give them the instant hiking options they would need. I am currently in love with this website: https://www.myswissalps.com/berneseoberland, even if we have no current plans to go there.

Best of luck to all of you in the planning...
AZ

A number of people have rightly commented on the need for doing laundry. While the comments to date have focused on locations and not accommodations, you might consider an airbnb or VRBO type stay in a few places. We have had good luck with that approach and it also makes the trip more interesting b/c you end up going to the grocery store, the wine shop, etc. and you can cook, rest, and do laundry in a "local" setting. Just a thought.

This itinerary seems exhausting. I can't help with the Switzerland portion, since I haven't been there since 1970, but as to the Italy portion, I agree with StCirq that Naples, as much as I love it, might not be the best place to start for someone not familiar with Italy. And the idea that three nights in Rome might be too much is just ridiculous, even if you don't love Rome, as I do. There is so much to see there! I think they will enjoy the trip much more if they pare down the number of stops.