If my dad and mom had a Will and then my dad died, does anything in the Will stand or can my mom change all of it?

If it is a joint will, that one single document covers both of them, then it becomes irrevocable once your father died. Your mother cannot change anything in the will since the modification of it would require consent of both of them. This is so problematic. Your mother should consult an attorney in your state to evaluate the will to find out.