My mom passed in October, before hand she won a worker’s compensation lawsuit. Unfortunately while waiting for her payout she passed. My brother decided to become trustee of her estate. Since then for no reason he stopped talking to me. Today I received a letter from his lawyer asking me to sign a notorized document stating that I give over my legal rights if any of her estate to him. Is it just me or does anyone else find this shady?

I wouldn't do it, not saying anything bad about your brother but you can't trust lawyers.