I had a BIL move in for "a little while" one time, and over 2 years later, he got mad and moved out. Thank goodness! It was horrible, he was not a good person to have in my home. Then the other BIL moved in with his family and stayed 5 months. I don't recommend it. In neither case did they pitch in for utilities or whatever.
Take if from me, "JUST SAY NO!"