A.: I understand what your sibling is saying, and I have no problem with it. There are legal matters to be decided here, and how long the family should wait depends in some measure on the specific verbiage in the trust. It's clear what your mother wanted to accomplish, and it's equally clear that you are concerned with your father's welfare.
You didn't mention how much money is involved here, but if other family members are in need of the money and you are not, why not go ahead and have the trust divided? The individuals who would like to help out your dad can do so.