How to remove benficiaries fro a trust?

I am the trustee of my mother's estate. There are 5 beneficiaries/siblings (incl. myself). My 2 sisters have been total obstructionists since the beginning and even filed a frivilous lawsuit (eventually dismissed) against myself AND my 2 othr siblings. Mom had the clause in the trust about bringing suit etc. My question-can I have the 2 sisters removed as beneficiaries?