Lets try something here.
Your brother is legally responsible as executor/trustee to file the necessary paperwork to get the money released to the trust so that the trust can distribute the money to the beneficiaries. Your brother, instead of doing it himself, decided to hire an attorney to do it for him. That is why your brother is the only person you can sue to speed things up, because your brother is the one who is legally responsible.
It doesn't matter how badly the attorney is behaving, its still your brother's legal responsibility. I don't get why you don't understand that.