Take the cat! Leaving for several days and not providing food, water or shelter is abuse. If I had to make a guess these people probably got her because the kids wanted her. The fascination soon wore off and out she goes. Unless she is really young I would think five pounds is pretty thin, but I also have a small five pounder that is very healthy. This is not the norm for most cats though.
If you do take her and the neighbors ask questions I would just play dumb. Haven't seen her and don't know what happened to her would be my attitude. People like that don't want the cat but they might fight you over her just because.
Ok, I know it's not good to steal, or lie but this is a life we are talking about. I hope and pray that God would understand and forgive under these circumstances.