I agree with Sunny. Let him go and see what happens. He is not
making progress at home and worse yet, evidently, he is getting
away with hurting his sibling. Time to let mother in law give it a whirl.
AND...by the way...try not to think negatively about mother in law trying. We have had more than one instance where loving parents shipped a
difficult child off to a relative and the kid thrived. It does not mean that
the parents are bad or stupid etc. etc. Sometimes a different
environment can trigger positive changes. Thank her for giving
her time and effort (even if you have to gag after you say it!)
because she really does not have to do it. If she succeeds...
time for a HUGE thank you. If she fails to find the key to him,
well.......that means the system will probably get a turn.
DDD