You are 4 times better off than your siblings. So they need the money you don't.
But it isn’t about money, it’s about feeling loved and being treated the same.
My DM gave my DB (never worked, his own decision - was kept by mum effectively) a huge amount as a house deposit (his wife borrowed the rest from her wealthy employer). I knew nothing of it, and when I did find out, her excuse was “You never asked for any money, you don’t need it”. Maybe that is because, like normal people, DH and I worked, we didn’t need her money but we could have been offered some!
It was so, so hurtful, it wasn’t about the money, but confirmation that she loved him more (he had always been favourite). She was by then terminally ill, and whilst I couldn’t walk away, it definitely impacted our relationship at the end.
It also ensured that DB and I have no relationship.
Op - As a pp said, at least you know now and can take it into account in coming years.
If I hadn’t accidentally found out, whilst mum was in respite care, my brother would have crowed about his good fortune when she died. I fully expected him to have changed her will too, and apparently he told her (in a letter that my cousin saw) that he wanted to as “he deserved it all”, but she stood firm on that.