Oh what a treasure you have!! I have an old quilt from my grandmom and had a person from the museum visiting our group. She said not to try to replace those bad or worn places, but to stabilize them using very find tulle. You can see through it, but it will protect those places from losing the batting or any more of the fabric. It worked very well for me. You hardly notice it when you look at the quilt. It just blends in and disappears.
Just keep them safe, they are a wonderful link to your family. Do they have labels? if not make sure you do something so that those who come after you will know who made them.. that information gets lost so easily.
(perhaps others have suggested the same thing, you'll get lots of good advice here!)