Uninviting someone over for Thanksgiving

Would it be rude of me to uninvite my neice and nephew over for Thanksgiving? Neither of them own a car, they would be coming along with my sibling. Is it wrong of me to tell my sibling not to bring my neice and nephew? Here is the situation as to why I do not want them coming along. I am wondering why my neice(17) and nephew(19) want to continue being gluttons for. My neice has a 26 inch waist, she weighs 56kg(126lbs) and she is 5'7. My nephew has a 28 inch waist he weighs 59kg(129lbs) and he is 5'6. They both eat 900 calories a day. Why are they gluttons? Should I uninvite them over for Thanksgiving dinner? They'll probably eat all the food before I can!

Unfortunately it's too late to give advice now. They most certainly aren't heavy weights from what your describing maybe they're on meth.