Hi- If you go with Windstar Line-use the Windsurf ship as it is the largest and has an elevator- the other 2 smaller ships do NOT have an elevator ( which may be required by someone in their 70's)..I LOVED the Windsurf as it is CASUAL ELEGANT in dress- Coat and tie are NOT needed at all , nor is any formal wear required...It is a 4 masted sailing yacht vs being a normal small cruise ship..so it is a very romantic ship also ---plus this ship hits much smaller and more out of the way ports-
IF your parents want to do the Caribbean, and use Windsurf, they need to be aware that most of those cruisers are into water sports as the back of the ship flips down into a marina with kayaking and windsurfing..Check the ports that the ship will be going into and make your decision accordingly.

OF the other cruises mentioned, You cannot go wrong at all with RADISSON--but it does have formal nites..and the PRIZE sailing vessel if money is no object is CRYSTAL....( and yes, it is more formal in nature and very upscale)...

"packet"...those ages are not old...lol. Look into Oceania...they are casual and no formal nights with five star dining.. The big plus is they are much smaller ships and getting great reviews especially for their food,because they are smaller they are able to get into ports that are less visited by the masses (which is a big plus)

Packet- Go to www.cruisecritic.com and look at their reviews-

Here is one on Oceania:

http://messages.cruisecritic.com/2/OpenTopic?a=tpc&s=927093444&f=069097554&m=59210975

Go with Silversea. Service is impeccable. It depends on what you mean by 'dressing up'. People aren't dressed like going to a Burger King, but casual enough. Formal nights is just nice. Ladies are in long skirt, pants or coctail dress, and not in ball gowns if that's what you are afraid of. They get the kind of service they were used to in old days. They'll love it.

I just read that the Paul Gaughan was ranked #1 of all the smaller cruiseships by Conde Nast (a well respected cruise magazine). Also, the dress code on the Paul Gaughan is all casual with no formal nights whatsoever. I have never heard or read anything negative about that cruise so if I were choosing, that would be my 1st choice. I believe they also offer "free air" during 1/2 the year.

Has anyone been to the eastern caribbean? (St. Martin, etc) How is it? Is it different than the western? What is the best time of the year to go?.

Has anyone had a bad experience with Silversea?

Being smaller ships, do they move a lot? Is the ocean rough in the caribbean?

Sorry for all the questions and thanks again for all your help!
Packet

Packet, I don't think you can go wrong with any of the cruise lines you're considering. I have never heard any complaints regarding Silverseas. As to the best time to go...my guess would be December, January, February.

If you're a bit concerned about seasickness or rocking, I'd strongly suggest you look at the Radisson Diamond. This ship is a twin hull and the vessel roll is only 1/5 of that of a ship with a single hull. It is far and away the smoothest ship I've ever sailed on. The entire experience is great, only a maximum of 350 passengers and the prettiest dining room of any ship afloat IMO.

Though they carry only 350 or so passengers, the larger Silversea ships, Shadow and Whisper, are big so you shouldn't have problems with motion. I haven't experienced any. I don't personally know about smaller ships, Cloud and Wind. Seabourn ships are small, so watch out, and so as Windstar. If sea sickness is a concern, book a room with balcony in midsection of the ship. Fresh air helps a lot when you are feeling the weather. You can't go wrong with either the Silversea or the Radisson. I've never had a rough sea in Carribean both Eastern & Western, but I think I've been lucky.