Thanks for all the support. I'm not really too concerned what the wife thinks, I guess I was just incredulous that someone could be so entitled to think we would do it.
DH is going to have a word with is friend, the husband, as he suspects that he knows nothing about the request. On the whole we get on ok as couples, although the wife and I don't see each other separately, only as a couple situation. Not because I dislike her, but she is one of those people who kind of takes over every situation. So, I guess I shouldn't be too surprised!
Speaking personally, if I were grandpa I'd be highly insulted that they thought so little of me that I could be shoved off onto anyone who would have me.