I think your instincts are right to have dinner. Just keep it simple: stew, something in the crockpot, spaghetti, etc. No need to get fancy if you are not in the mood. For those who do the big turkey thing at Christmas, I think it's great but gave that up years ago. (The only reason I think it's useful is for the leftovers, so that's a consideration). Can you tell your SIL to bring dessert? If not, buy it or get some cookies and ice cream. Serve packaged rolls. There's no law that says how elaborate the the meals need to be.

For breakfast, either leave them with cereal and toast and lunch fixings for later. A turkey breast, which is much less trouble to cook than a big turkey, is good for leftovers and lunches. Done.