Ongoing Family Fall Out

[Chrimb0953]

AIBU to feel fed up of years of family issues?

Mum and Dad divorced over 20 years ago
Dad was incredibly cruel to my mum emotionally.
Dad has remained difficult towards mum whenever he's in her company and this has been uncomfortable for all around, yet dad tries to use me to find out about when he can, as I think he hankers after her - unbelievable really.
In the meantime my sister married someone who changed her beyond recognition because everything is very much about him and his way of living life, so sister has morphed into a 'mini him' and is utterly unrecognisable. I no longer have contact with either of them (or my young nephew), as us adults just don't get along.
Despite showing the utmost kindness and respect Mum has also had massive issues with the 2 of them and now no longer sees them and has been banned from seeing the only grandchild she has, which is obviously heartbreaking.
A such, l no longer feel able to continue a relationship with my dad, when my mum is being treated so cruelly, as I believe he shares some responsibility for the situation. This means the relationship between me and my dad has now broken down.

AIBU to feel dine with it all? Why do 4 people in a family end up with so much anger and bad feeling towards each other to the point where the family just breaks up? Any thoughts?

How often was he actually in her company if they divorced 20 years ago?
you saying your dad shares some responsibility for the situation, you mean the situation of your DM no longer seeing your sister and grandchild? I’m really confused.

They are/have been in each others company for graduations, birthdays, weddings Easter, Christmas and when visiting grandchild etc. Not for long but enough time for dad to pretend my mum isn't in the room, grind his teeth, speak through clenched teeth when he had to talk, walk out of the room etc.

Yes, I believe my dad has had a lot of influence on my sister. They have become incredibly close and are now very aligned in their views and approach. I have no doubt that he has no qualms with the fact that my mum has been banned from seeing her only grandchild, whilst he is seen as the golden boy with full access and little reprimand for the way he has behaved and does behave toward mum when he sees her.