We haven't had this happen but the last 3 generations has had this disagreement in our family. And it's caused issues everytime.
My great grandma wanted to leave everything to one granddaughter (there were 4). My grandad and her had an argument. He told her she was not treating the rest of his daughters like that. He told her it was either left to all 4 of them or him. He knew it would cause a rift between his daughters. His mother's agreed
That same grandad, when he got older then threatened to leave one daughter out, for really petty reasons. The others simply pointed out they would share it equally, but the hurt he would cause would be horrific. Then he was splitting it between the daughters but based on how many kids they had. So 2 daughter got substantially less, my mum ended up with the same and one ended up with more has she had 4 kids. As my mum was impacted she said that the only fair way to do was to split it 4 ways between his own kids. He agreed. But there was a lot of hurt as the one daughter with 4 kids has always been the 'golden child'. Mum said at the time, that in her opinion people can do what they want with inheritance but her opinion was it should be split equally between the persons children. Still, 2 sisters no longer speak to the other 2.
And recently, mum and dad have decided they might share theirs unequally. Or might leave it to the grandkids. I told her she could do what she wanted, but I thought it was hypocritical, after what she said about my grandads inheritance.
Turns out this was sils suggestion based on the fact that sil had just inherited a large sum from her estranged father. And would inherit from her mother. She had sat mum and dad down and told mum and dad it would be irresponsible to give me and my brother the same. It would cause problems in their marriage if my brother inherited sustainably less since she was inheriting so much. And they would be causing their marriage problems because of the disparity. Mum and dad felt bad.
Its not the first time she has tried to tell them what to do with their inheritance or who they leave sentimental items too.
Mum and dad have since decided its just getting split 50:50 between me and my brother. I just know, though, that when my parents die SIL will cause that many problems, I won't speak to them again. She keeps insisting she wants some of my nanas jewellery, that mum has that was meant to be mine. She never even met my nana.
I hate talking about my mum and dad dying and I wish they would just spend it all now. I hate how much inheritance has caused so many issues. I told mum and dad I won't stop speaking to them if they decide to split it different, but to remember what happened with my grandad and how they felt at the time.
Although tbh, I don't like my sil (she told me women who work and plan to work after having kids, should be made Infertile and should not be allowed kids. I was a working mum) and the thought of her planning the aftermath of my parents death as she has been very cruel to them in the past, pissed me off.
I hate inheritance. Its caused so many issues in my family. I am leaving dp some money and the rest is going to the kids. 50:50. If I am not with dp or he dies first just the kids 50/50. That's it.
I can't imagine how painful it to havevig actually happen. Wether people agree or not, for most people splitting it so unfairly (unless there's reasons such as one has substantial medical needs) does leave the message that one child is more worthy than the other.