I would agree that you probably shouldn’t keep them. I’ve encountered a similar problem in our collection, with a donor who gave a significant amount of money to our repository and then felt we should accept any books, however, unrelated to our collection they were. We spent a long time working out a collection policy, sent it to you, but she continues to ignore it. After many years, we finally have accepted them, set them aside and will eventually sell them. Not a good solution, but the best we could come up with in a tricky situation.