Sometimes it's better not knowing IMO.
Like I don't want to know about past relationships my fiancee had but if it comes up I won't freak out saying I don't wanna hear it or anything.
I don't want to know about my Dad's sex life as a youth is another example of this, I don't want to know if my parents did drugs as youths etc...
Just some things won't be a benefit to know so what's the point I guess?
In one aspect I can understand where you Mom is coming from since she doesn't what your memory of your father to be tarnished but on the flip side, if you do want to know then I see no reason for anyone to say otherwise.
I know you've just been through so much here and I'm sure your head is spinning with all sorts of thoughts but maybe finding things out down the road might be easier to handle than right now with all factors considered?
My my opinion though, take it for what you will.