AITA for insisting my brother and I share his inheritance & for not giving any to my niece?

I (20M) have a brother (32M). He is chronically ill, and has extensive medical expenses, which are covered by the local government. He was kicked out of his mother in laws house (where he lived with his wife & son), and my parents (who I live with) took him in. My parents pay his groceries & phone bills, and my brother and I split our parents local restaurant bills, since they can't afford to take in a third person. I give my brother money whenever he asks for it (going to a bar, a concert, traveling, etc.)<br><br>My grandparents left behind a 1 million dollar inheritance, with my brother & I as the sole beneficiaries. The will stipulated we'd divide it equally (outside of a 10% discretionary amount our parents could divide as they pleased). I became of age recently and received my share. My parents gave my brother the 10% from my share, and used the rest to buy gifts for themselves. When my parents asked me what I'd do with the inheritance, I said I'd follow the will's instructions. They said it'd be unfair to my brother, since he has medical expenses, where as the money would be wasted on me, since I'm otherwise healthy. I said they could give him a portion of what they took from me, but that didn't go over well. Now my brother is going around telling everyone what a terrible person I am. AITA for not giving my brother more of the inheritance? I'd also like to add my parents pay for my niece's (brother's daughter) college tuition (my parents don't pay for mine), and a part of the reasons they say I should give the money to my brother is so that my niece could have more money for her studies.<br><br>Edit: My grandmother passed in 2019 and my grandfather in early 2020. Both died before Covid hit. The 1M is before taxes and fees and such, I think I have 0.9M total, since my grandfather didn't leave any debts or have any loans, so there wasn't much to pay. My brother's wife is a SAHM and my niece has two older brothers. I'm not my brother's caretaker, he doesn't need one (he's chronically ill, not handicapped), and he's never given me money (I've given him money on several occasions). I don't mind paying for my niece's education. My parents pay for two older brothers as well, so that makes me the third.