Thats fantastic news for him - he is so lucky to be just 14 - he has time to get out before they screw up what precious little youth he has left
I think whilst the sister idea does seem like a food idea on one hand - the fact that it's YOUR sister means you're probbaly NOT gettign off the hook for this - remember BLAME (along with fear) is what dubs feed on .....so you may as well just let him stay with you.