Yes, janisj and Gardyloo, LHR - EDI is a separate economy ticket. I am assuming I would lose my money on that ticket if I cancel (I haven't checked into the details yet). Maybe I will wait it out like you say, to see if it gets a schedule change.
If I follow Gardyloo's suggested itinerary, I will be renting a car in Aberdeen and returning it in Edinburgh. That, in my experience usually means a big jump up in price. I'll need to check into that as well. Pennan sounds and looks beautiful! I will take Skye off the itinerary and look at the Oban Three Island tour suggestion.
You guys have given me lots to work with. Thank you both so much.

I have rented countless cars in the UK (mostly via AutoEurope but maybe 25-ish% directly through the rental companies) Only 3 or 4 times have I been charged a one-way drop off fee. (Now, the rental car landscape has changed a lot since 2020 so drop off fees may be more common now. My last trip involving driving was in 2019). But even when there is a drop off fee, it usually isn't very much, and a one-way rental often makes for much more convenient itineraries, much like open-jaw flights. Avoiding a drop off fee might be a false economy.

IME, the biggest hit on UK rental cars is booking an automatic transmission (luckily I prefer a stick -- so I've saved hundreds of Ł over the years)

Good to know! DH and I can both drive a stick, but I'd prefer not to with the driving on the other side of the road obstacle. Ha

Any change fee would depend on the fare basis/booking code of your ticket but probably would be on the order of Ł50 max. I'd phone the Airline to see.

A quick look on Expedia shows a one-way rental (ABZ - EDI) on an automatic SUV for your dates would actually be cheaper than one picked up and dropped at EDI. The savings would amount to around Ł15 - Ł20 per day, so for four almost as much as the plane change fees.

Oh by the way,

Not trying to brow beat you into hiring a standard transmission - honest. But just giving a different perspective. The conventional wisdom is an automatic tranny is safer/easier/'I just can't imagine shifting with my left hand!".

But I am in no way ambidextrous and totally right hand dominant yet have no trouble at all shifting with my left hand. Its hard to explain, but the times one can get into trouble are mostly when your attention wanders a bit -- easy to do with all the wonderful scenery. Instead of drifting into 'autopilot', having that pesky gear shift there on your left side just keeps you on your toes. Besides - you ain't trying to pull someone off the line LOL -- just gentle up and down shifts. Plus modern transmissions are pretty sturdy -- missing a few gears won't hurt anything

Again -- opting for an automatic is perfectly understandable -- but a stick wouldn't be that a big problem (you'll find that most who say get an automatic either haven't driven a stick on the 'wrong side of the road' - or really aren't confident with a stick even at home)

Gardyloo and janisj...I have revised my itinerary to better accommodate our time in Scotland by using many of your suggestions. Please comment.

May 13 - JFK - LHR (daytime flight) Spend the night near LHR.
May 14 - LHR - ABZ No flight booked as of yet, but we will probably get an early morning flight into Aberdeen. Rent a car and drive to Cruden Bay. Arrange a golf tee time for early afternoon. Sleep in Cruden Bay. I think playing golf on that day is a mistake, but DH insists he will be fine to play that day.
May 15 - Drive to Nairn, stopping by Glen Moray distillery on the way. Sleep in Nairn two nights.
May 16 - Excursive options near Nairn ...Culloden Battlefield/Cawdor Castle/ Clava Cairns/Glennfiddich Distillery. Second night in Nairn.
May 17 - Drive to Glencoe...Visit Urquhart Castle on the way. Sleep in Glencoe two nights
May 18 - Excursive options near Glencoe...Glen Etive Road, Glencoe Lochan Trail, Clachaig Inn. Second night in Glencoe.
May 19 - Drive to Oban...Oban Distillery. Three nights in Oban.
May 20 - Visit the islands of Mull, Iona and Staffa. The West Coast Tours "three island tour" is a very long day. What about visiting Mull by it self. Worth it? I get seasick easily. Are the ferry rides rough? Second night in Oban.
May 21 - Side trip from Oban to Kilmartin Glen. Other recommendations for Oban area? Third night in Oban.
May 22 - Drive from Oban to Edinburgh. Sleep two nights in Edinburgh.
May 23 - Side trip from Edinburgh to St. Andrews and then to Scotscraig for souvenirs. Back to Edinburgh for our last night.
May 24 - Very early flight back to the US.

Should I take one night away from Oban and add it to Edinburgh?
Thank you one and all for your suggestions and recommendations!

Great that you are flying in to ABZ . . . Started reading but just remembered I have to get a move on so i'll finish later but just a quick comment about May 15. While Glenfiddich is far from my favorite single malt, their distillery tour is terrific, one of the best. Maybe consider doing Cruden Bay > Dufftown/Glenfiddich > Elgin > Nairn. Almost the exact same drive time and you could still visit Elgin Cathedral en route. Plus Balvenie Castle is about a 1 minute walk from the Glenfiddich car park.

Great! Good to know. I'll change that as well.

Back . . .

May 14: I would book a late afternoon or early evening tee time. Sunset on May 14 will be about 9:30 PM so I'd be booking no earlier than 4PM but 5-5:30 would be fine. I'd not want to hassle with LHR, fly up,, deal with car rental, drive to B&B, rush lunch and dash to the course.. Fly up in the AM, get the car, check in if the room is available or leave bags if it isn't. Do some easy sightseeing practically in the village (google both the Bullars of Buchan - amazing, and Slains Castle). Have a leisurely late lunch (or early dinner) . . . THEN walk over to the course.

Re your Oban/Mull conundrum. If It was me (just me personally) I'd drive from Glencoe to Oban and take a noon-ish ferry over and stay two nights on Mull. There is a lot to see/do and it is a large island with slow roads. Duarte Castle, Iona, Staffa, Calgary Bay, Tobermory town and distillery. You could stay in either Fionnphort (my fave) or Tobermory. If in Fionnphort you can walk on the foot ferry over to Iona and catch boats to Staffa from the same pier. IF there is availability (they are usually booked up well in advance) look here https://www.iona-bed-breakfast-mull.com HIGHLY recommended. Great food, great views.

More re Mull -- Take a mid-day - do not take an early morning nor late afternoon ferry. Because. . . . that is when the day tripper coaches arrive and depart the island. You do not want to share the road to either Fionnphort or Tobermory with large coaches.

Re the ferry ride- I've only been seasick a couple of times in my life so may not be the best judge. But I've been to Mull 4 times (one day trip and 3 multi night stays) using 3 different ferries and have had no issues. It is a fairly sheltered channel and the Oban Ferry is large (the other two ferries not so much . . . But they aren't relevant to your route). And the foot ferry to Iona only take 5 or 6 minutes.

Oops . . . Duarte Castle . . . where the heck did the Spanish come from

I get seasick easily. Are the ferry rides rough?

Most of the these inter island ferry trips are in protected waters but it depends on the tides and the winds on the day and in the previous day. If you get seasick very easily then, you may this time too.