Anyway, she recently phoned and asked if they could stay with me overnight as they were attending a wedding near me in 10 days time. I said yes, of course, then she asked if actually, could they stay for two nights - The night before and after the wedding, the whole weekend?
Yes, she used you for accomodation, but on the other hand, that is what she said she wanted? If someone said something like that to me, I would assume that they were there mostly for the wedding, wanted a free place to stay, and would spend a little time with me. I would then agree to that or not agree to that. You seemed to have been expecting a proper visit, which she never said would happen.
I have to agree with bopper. If a friend called to ask if they could stay while attending a wedding, I would expect them to be so busy with the wedding and associated activities, even unplanned ones, that I would kind of expect to be treated like a hotel. That being said, not cleaning up after yourself is rude. She could have at least tried to minimize their impact on your house.
I agree with this, to a point. I might not expect my guest to be able to spend a lot of time with me, as they purpose for their visit is a wedding, or some other event. That being said, I would at least expect them to clean up after themselves, say thank you in some way, and be a gracious guest, none of which the OP's friend did. They let their kids run wild, did't pick up after themselves, and expected the OP to have stuff in case their one child wet the bed. Not good guests.
I know I will sometimes stay with my cousin on the way to my mom's, and while the visit is short; I usually arrive in the afternoon, beforer she gets home (I have a key) and leave very early the next morning, I take care not to make a mess, strip the bed, and put my towels and sheets by the laundry, and also offer to take her out to eat, which 9 times out of 10, she declines, but I offer. Or I'll bring something with me, that she can't get, such a bagels, as a thank you.