I'd say it's possible to get your dad to maybe soften a bit if you have a formal diagnosis, as these sorts of people tend to respect the perceived hierarchy. But if your mom is a psychologist who is deeply ableist, that's asking for her to deny that any diagnosis is valid. It seems like that would probably be a difficult combination to get through.
If your siblings have phones or other technology, you could reach out to them independently. My partner has done a lot to help her younger sibling not turn out like her parents (chuds).
I personally wouldn't feel obligated to put myself in that position with no support. If they want to know why you don't want to come, you could be honest or make something up, but you have value independent of your family, so fuck em if you don't want to put yourself through going.
Hope that helps comrade.
