this thread has legs! fabulous information! :)

Kathleen and Sue: Many thanks for taking the time to offer helpful information. I will look into the suggestions and take a look at the various rental sites. I think I've mentioned that I've been renting in South Florida for the past two winters but am interested in broadening horizons..

Jojo: I have not stayed for any length of time in Charleston for about 20 years (used to travel to the Low Country for work fairly often). If the engaged couple are looking for a luxury property with on-site spa, and accommodations in separate cottages about as large a my home in Manhattan, they might want to take a look at Palmetto Bluff, in Bluffton, SC. Easy to do daytrips to Savannah and Beaufort from there, and to Charleston as well, I believe.

It is upscale, with rates to match, but they do offer relatively reasonable rates in winter (we've stayed en route to Florida and each time we come to love that area more). It might be lovely for a wedding, or even for the first part of a honeymoon, with the idea that they could move on to Charleston after a few days. The room are really beyond wonderful, and the setting on the May River is divine.

http://www.palmettobluff.com/the-inn.aspx

Wherever you choose in December, I would imagine weather would be lovely as long as you do not plan to swim in the sea, as had been noted my the locals posting above...

I spent my honey moon on Sullivans and I ended up moving there : D! jojo, tell your friends to get ready to fall in love.

Charleston is beautiful at Christmas. The Wentworth Mansion is very traditonal. Harborview Inn has rooms with views, but you have to specify that you want it. And Charleston Place is beautfully decorated at Christmas.

I aree with eks that Palmetto Bluff is a very rounded development with excellent service.

Suewoo

There is something odd about Sullivans, it just feels safe to swim there and feels more like the UK waters.

I would need a cage to swim in the sea down the coast on Edisto, it just feels far more rustic and I have seen far to many monster sharks hauled out by surf fisherman. Just can't face swimming there.

Charleston is beautiful at Christmas. The Wentworth Mansion is very traditonal.

----
We stayed at Wentworth last week and it was absolutely fabulous.

Dickie_Gr, Sullivans is where we spent our honeymoon. My friends have a house there. It may feel safer, but believe me, there's all kinds of critters in the ocean! I don't think Edisto is any more dangerous. I love it down there too.

saving to re-read

I like Charleston and i liked it when I lived nearby back in the 1960's. Would I spend the Winter there? No.

Because it is too cold, right?

I think "cold" is relative. I think the OP is from up east--and "cold" there is not Charleston "cold". However we have just had a big cold snap down here--and today it is gorgeous, the cold front has moved up the coast with snow and it's a nice 50*.
Sunshine matters too. Our kids live in Denver and while it is cold, they have 300 days of sunshine.
Depends on what "cold" means to you.

The weather seems really odd and probably is a function of its geographic location.

We had wonderful weather in October this year : mid 80s.

Then on the last day it rained and struggled to 45.

The lows seem to fall down from the north to push out the settled weather. Locals talked of 80 on Christmas Day some years but a whole lot colder many years.

We are keeping tabs on the winter weather to see ow Charleston moulds into our 3 country retirement plan.

The heat in summer is shocking for Northern Europeans we just couldn't cope with the humidity of the marshes.

Humidity IS to be dealt with--I have referred to it as a "mildew alert"! But on the beach? Very pleasant, but HOT!

Actually -- they stayed in the historic district at the King Charles Inn. They loved it! Loved the whole & said they were treated royally wherever they went.