One of my son's briefly lived with a woman who had 5 kids (thank God she's long gone now!). They got evicted, and she called to see if they could live here 'for just a few weeks'. - she also just sat and smoked when they'd come for a visit, and never watched her kids (ages 7-1) - said it was 'her' break time! Gee - I don't remember offering to watch them!
We have a very small ranch, and the 7 of them (+ 2 dogs, 2 cats) would have completely filled this house! My son always knew he could stay here whenever he needed to, but I didn't owe the bimbo a thing. Everything we own would have been fair game, taken over, and destroyed. Not to mention DH & I would have had 5 kids to take care of while she was off to Walmart, or wherever constantly!
I just kept repeating the same words, "No, I don't think it would work out very well." as she kept countering it'd just be for a few weeks, we don't have any other place to go, etc. Well, guess what - she found another place! Moochers always do. Sad, sad life for her kids though. :(
Stick to your guns, and know you don't owe anyone a reason!
:)