how to remove a co-trustee from a trust who refuses to resign

upon my father's death, his will provided that his assets be put in a trust for my mother. The lawyer who set up the trust made himself a co-trustee with my mother as the other co-trustee and has neither advised on the trust and has had no contact with my mother in over a decade. He became hostile when he was asked to resign so my sister could become co-trustee and refused to resign without being paid a significant amount of cash for which he has done nothing in 30 years. Can we have him removed?