I would keep them for my children. Declutter the other stuff in your house. There's honestly not a lot of "stuff" in my home, I'm not one who kept every yearbook and souvenier of my life. But there are some things that should be passed down. I keep my mil's trifle bowls in a place of honor in my china cabinet, right up front with my OWN china (though they aren't the same pattern) out of respect for my mil and for my husband's family history. Pass them on when one of your children gets married. It doesn't have to be the only wedding gift, but you can pass it on as a memory. I don't see the problem with a set of glass cups. I'm sure it's not going to ruin the cleanliness of your home, and I doubt it's the only thing that could be thrown out in your home. Why hurt her feelings, possibly your husband's, or throw out something that has been handed down a several generations? In the meantime, USE them! I use my china for holiday meals, anniversaries, Valentine's day, and any other time that an "adult meal" can be served. They can mean more to you if you just have an ice cream party....or a family tree party where you eat ice cream or trifle in them, have some special drink from another side of your family, or special recipe(s), and look at pictures and talk about people, tell a little history and some stories about who people are. That way it'll mean something to you because you've got some context on who gave them, but also they can mean something to your kids too, because you've built a memory. If it were MY mil, I'd even serve it to the family while she's there and ask her to talk about the grandma she got them from. No, technically value isn't in "things" so much, but you can be gracious and make some attempt.