How does being a psychologist constitute a reasonable qualification to have any weight on the matter? Vaccinations belong to the field of pharmacology, on which psychologists have no training whatsoever (possibly aside from psychiatric drugs) and if they do, they're most likely a psychiatrist, in which case they're doctor first and psychologist second.
The author has no qualifications whatsoever to talk about vaccines, aside from her doctoral dissertation, which I would consider questionable at best.
I can relate to you, having gone through something similar when I graduated about 20 years ago. My mom was also the one who thought it was important at the time, kind of like a coming of age thing, and while my dad wasn't all that interested, he absolutely wanted to be there, and absolutely did not tolerate my mom or her family.
So the way it worked out was that I bounced between my mom and her family, and my dad and brothers. While I felt a bit bad at some points for leaving my dad alone when my brothers went to talk to our mom as well, or that he ignored her and only spoke to my grandma, he kind of chose that for himself.
I had already made plans beforehand with my mom to celebrate a couple of days later with her family, so after the whole shebang (had no interest in partying), I went back home with my dad and brothers, had a smallish celebration and that was that; family pleasing done, and I had a relatively nice experience in the end, with little to no friction between relatives.