These are charming. Not sure what they're made of and I'm not an expert at textile preservation, but a highly trusted dry cleaner should be able to spiff them up. I presume they're wool? Professionally mounted in a shadow box (according to your taste and the era of the mittens) would be worth the investment. If you intend to keep them, and you should, if you have any winter-sport pictures of your ancestors, a skilled framer should be able to help you compose something very special, a fantastic legacy item for your family. Be sure to write the history on the back!
We had some old pieces of tatting from an ancestor, we mounted them in shadow boxes on old coral colored silk. Very special.