C.W.
Strange, I have never heard of a Will not executed immediately/in a timely manner, upon the death of the person.
That is what a Will is for. It is especially important to do this under YOUR circumstances. Odd that he would think he had a say in another's Will. He does not. I see red flags all over the place.
Absolutely get a lawyer, immediately, and if you need a rec, I can supply one......(I have a close friend whose husband is a prominent divorce attorny and he would know who to call) if you need one.
Do this for yourself AND for your Mother.