Nowhere is it written that YOU have to do everything to get ready for Thanksgiving. Everyone in the family needs to pitch in to help get it all done. Have a meeting, discuss all the things that need to be done to prepare & then ask each family member what tasks they would like to do.
If all you get are excuses, relax. Rather than getting upset, just take a breath & let your family know that they will be enjoying Thanksgiving dinner at a restaurant this year. No threats. No sarcasm. Just tell them in a matter-of-fact manner. AND MEAN IT! You are busy too & you should not have to shoulder the responsibility for all the work.
Everyone enjoys the meal. Everyone should help. Be strong! You will be doing a lot of work so there is nothing to feel guilty about. Thanksgiving is a family event. The family should help prepare!