((((((((((( lenjan )))))))))))))))
I'm so sorry that they are trying to continue the one-upmanship over you in this situation. I think it goes to show who the really ill ones are.....it's them!
I'm willing to be that some of the reasoning behind this is that they feel guilty, that they are trying to hide something (their guilt) and they have this horrible need to be what they consider, first in his life (at 21 no less *sigh*). Yep, they be jerks alright.
I know it's hard to always have to take the high road and bite your tongue when what they really need to hear is what jerks they really are. I can pretty much guarantee you though that this high road you have had to take is going to pay off in the long run with your son.
Hon, just see him as planned (at least you have the holiday time!) and be your wonderful, caring self with him. Continue the high road by not dissing his sperm donor and his parents. Keep your discussions on the two of you and enjoy the time you have together like no other. There will be plenty of time in the future for him to see who is who and if he is anything like his mom....he will figure out what's going on for himself.
In the mean time, I'm sorry for the stress, anger, pain you are going through right now. The frustration alone would drive me nuts I'm sure. I'm sure once you can concentrate on your relationship with your son, nothing else will matter!
Take care dear one!

sabby