My grandparents had always been quite clear what they wanted done with their estate. Contents of bank accounts shared between their children (2 brothers). Value of their house shared between their grandchildren (4 of us).
Granny died and Grandad remarried (this isn't going where you think). Step-granny had nothing. My dad and my grandfather and my uncle were estranged.
My grandad became frail and my step-granny had always been a bit pathetic. So my uncle convinced my grandad to sell the house and buy a big house together that they all (uncle & aunt, grandad and step granny) would live in.
Grandad died. Step granny's daughter arranged for her to go into a Salvation Army care home (in an attempt to get her hands on grandad's money - she failed).
Uncle and aunt, and by default, my cousins got all of the inheritance. I know this was deliberate, because the one time I saw my aunt with my mum after Grandad's death, my aunt discussed 'Our children's inheritance' (meaning myself and my brother and my cousins). My divorced parents did nothing about it and so my brother and I lost all of our inheritance.
What would you OR your parents have done? Was doing nothing the right thing, because it was too complex to disentangle? Or should they have fought it?
I was a very young adult at the time and it didn't occur to me we should have done anything. Incidentally, my uncle is still alive and has remarried a woman with nothing after my aunt's death. My cousins definitely benefitted (house deposits, cars etc).