Yes, I get it OP. My only advice is to let it go because otherwise, the anger and frustration will hurt you far more than anyone else.
It sounds similar to my mum and Aunty’s relationship. Aunty was the older one and got everything and mum was expected to be grateful for the leftovers. Granddad was kind but grandma was nasty especially to mum’s 4 children, which I was the youngest. I don’t think grandma wanted more than one child bus I suspect that granddad wanted a son, so mum was a double disappointment.
When grandad was old and too ill to manage his business that he’d built up from scratch, Aunty’s husband stepped in and took over. They had a ‘gentleman’s agreement/handshake’. The business was run from land that included grandad and grandma’s house. The deal was that both could live out their days there. Within 5 years, Uncle had sold the entire business for a huge profit inc. granddad’s detached house and garden. The grandparents moved into a council flat that the local vicar helped them get otherwise they’d have had to find a private rental property themselves. (This was the early 70’s)
Grandad was furious and vowed to have nothing more to do with Aunty and Uncle but he died suddenly a year later leaving grandma who had dementia. Uncle turned up and cleared the flat of anything valuable inc. the old grandfather clock that I’d always loved. It had horses carved on the top. Grandma moved in with us and mum had to reduce her hours at work to look after her. Grandma was difficult and incontinent too. Aunty had never worked a day in her life and refused to look after grandma even though my mum couldn’t afford to earn less money. Eventually, after about 2 years, my mum was pleading with Aunty on the phone to have grandma for a couple of weeks respite and she agreed. They collected her and then took her straight to a nursing home. Grandma died within that 2 week period which looking back as an adult, I feel was highly suspicious as I don’t think she has been physically ill, just the dementia.
Mum never received a penny in inheritance. The only tiny bit of Karma was after my mum died. Aunty came round to see if there was anything she might like to have of mums (my kind older sister let her have a rummage!) and she was looking through my mums wardrobe. Mum wasn’t particularly well off during her life but she had an eye for a bargain and naturally great taste and was a slim size 10 whereas Aunty was about a 16 and always dressed frumpily. Aunty said how much she admired my mum’s style and confidence and wanted to have some of mum’s clothes. We were going to charity shop them anyway so told her to crack on but she’d never have fitted into anything of mums.
My sister and I thought it was hilarious and imagined mum laughing her head off hearing that Aunty admired her as she’d never have admitted that to her face, ever! 😂
My very kind sister carried on visiting Aunty in her care home after she was widowed and despite all the wealth, Aunty wasn’t particularly happy. We also heard that Uncle was a womaniser too all the time they were married.
Honestly OP, you won’t win so try not to let all this hurt eat you up. My mum managed to let it go and focus on her own family. Take care. x