Sure, there’s no need to need to punish yourself by sitting around deceptive people, old or young. I agree psychopaths don’t need emboldening.
But come on dude, these are his literal parents. No matter what happens, your family should come first. This is one of the basic problems in the Anglo sphere West, we have stopped caring for being families and end up totally atomised. In these times especially, we need to keep our loved ones as close as possible and forgive SOME of their mistakes. These people are not inherently evil or psychos, they are brainwashed, and you know the spell the media has cast upon them. And it doesn’t have to be so black and white to conclude they have deceived on purpose. Maybe they tried hiding it because they knew he would be hurt. Of course, it is a problem they clearly treat him like a child. But you know we all engage in innocent deception sometimes. For example, telling our children Santa put the presents under the tree or whatever.
I would loathe to think about my children ostracising me when I’m old and maybe clueless, based on what they think is right (even if they are right). I don’t like punishing people for things that are not their mistakes, not entirely. You know how the media has a strong hold on some. If these were not his parents, I would have definitely told him to not give a mosquito bottom.
Re presents, I think it’s almost important to get presents for your family on Christmas. It’s the only little enjoyment we are getting in the year. I have boomer parents myself, and I have resolved to not talking about politics or vax or anything deep, really. Just exchanging pleasantries and presents. Barring them from family because they are brainwashed is just not right!
All I am saying is that everybody in this life has a responsibility to treat others with dignity and respect. The only people who get a pass on this fundamental requirement of humanity are children (since they haven't learned much about life yet) and demented people (since they are mentally gone and don't know what is happening). Old, but cognitively intact, people definitely do not get a pass. If there is no reciprocation in respect/care then everything falls apart.
Again, I am not saying they should be punished but this behavior should definitely not be encouraged either. It's tough, I hope I don't sound like I have the answer to this riddle. If it was me, I would probably give it a go to spend Christmas with them but if I sensed generally fake niceness and duplicitous behavior, I would probably leave after a few hours and go spend my time with people that want to genuinely be with me. A sense of duty is only meaningful in regards to people who can appreciate it. Parents do not magically get a pass for being jerks just because they are parents. Neither younger people not parents should take the other side for granted and behave as if the other side owes them something. That's all I am trying to say, and that's why I was phrasing my post as questions instead of saying "he should be doing X".