We have stayed at CSR twice now...and our college-age daughters are there right now! (and having a great time!) We stayed in Casitas the first time, and business class just this last October.
I am also a mom of twins (those are the college students now!)
I think staying business class makes perfect sense for you. It was always nice and quiet in there, plenty of space for everyone, and we enjoyed the refreshments provided. Keep in mind that it does close at ten, thought I'm thinking your little ones would be in bed by then.
As far as bus stops go, I'm guessing you'll have a stroller? I would just walk over to the Casitas bus stop in the morning and get on there. (they have the first stop). It's probably a 5 or 10min or so extra walk from the Business Class building. Then when you return, get off close to your own building. We have never stayed at Christmastime, but even in the Fall during Food and Wine and the Halloween parties, we never had a problem with busses. Honestly, never even had to stand!
Good luck! Have a magical trip!