It sounds like a pretty easy solution to me, you have you own needs to worry about. As bad as you feel you should probably distance yourself from them, I don't know what their resoning for not having any family but i looks like they have been playing every one in you complex (and probably did it that last place they were at) some people are just shady. That whole milk and cereal thing would have done it for me, sorry.

We have a saying in the Marines,"No better friend, No worse enemy"
I am all for helping those in need, family, friends, stangers. but screw me once and you better not come back, cause I aint the one. Unfortunatly sometimes once is all they are looking for.

I apologize if this seems harsh but I have met some shady people that had great stories, and until I can verify those stories I gotta error on the side of caution.