We just did the same thing this past Thanksgiving w/ DD9 and DS5. Flew in from RDU on Friday, had time to unpack, get groceries, and go swimming and relax on Friday. (We got to Orlando around noon) We stayed in our timeshare until Thursday.
Saturday, we went to MGM. The crowds were very low!!

We did FP and baby swap for TOT and RNR, we saw the Power Rangers and pretty much did everything except for Indy Jones and Star Wars (been there, done that, don't want to do it again.) We still ended up w/ time to do RNR w/ a baby swap before Fantasmic.
Sunday we went to AK and the crowds were about the same. We used FP for KS and lines for everything else wern't bad.
We took Monday off.
Tuesday, we went to the MK and it got crowded!!! We just made the best of it and used our FPs wisely. We did the Char. dinner at CP and stayed until the late fireworks. It got a little cool Monday and Tuesday, but not bad at all. The cast members were laughing at DH and I b/c we had on shorts, but we told them considering it was in the 30's at home, the low 60's was a heat wave! (We were fine in shorts during the day, this was just later at night after the sun had gone down.)
Went to EPCOT on Wednesday and it was crowded also, but not unbearable. Again, make good use of the FP! We got all of Future World done, but not much of World Showcase. Be sure to get a good seat for Illumnations. I think we got one about 30-45 minutes before the show. (At least until DS decided he had to go to the bathroom and DD and I were in Mexico and DH had to leave our spot!)
We took Thursday off and it was warm enough to swim. We were going to have Thanksgiving dinner at Bob Evans, but they were closed so we ended up at Benigann's. (It wasn't too bad-they had a Thanksgiving dinner special). We also moved over for 2 nights to the ASM resorts. The kids and I took the bus to DTD that night. It was very convienent, especially w/ DH not wanting to go.
Friday morning, we did the EMH and got to the MK at 8:00 (or whatever time they opened) and stayed there for a while, doing repeats of our favorites and catching whatever we missed on Tuesday. It was fairly crowded, but not awful. We went over to EPCOT in the afternoon and did the games and stuff in Future World (the name just excapes me!) and then headed to WS and finished up there. We went back to the MK around 9:00 to catch the fireworks again.
The crowds did increase as the week went on. My advice is to make the most of the beginning of the week, so you aren't trying to get a ton of stuff in at the end of the week. We usually go in October, but wanted to use more of the kids school vacation. I am sure we would go at Thanksgiving again.
Sorry this is so long, but I just wanted to pass our experience on. Let me know if you have any more questions.
