As your MIL is putting her son first and formost wanting it all to be easy for him, wanting this nighmare which he created to just go away by you allowing him to just come home. You need to put your kids and yourself first as well no matter how much you feel you are hurting both of them (your husband and his mother).
I would not remove the restraining order, he's done NOTHING to warrent you dismissing it.
I would not allow him to move home, he's still not admitting he even has a problem.
It seems he is still calling the shots with all this. He doesn't want to move in with his parents, he doesn't feel he needs help, etc. etc. The easy life of an addict, get out of trouble with help from mom, make it al go away so I can just get back to my normal life. A life that includes low self esteem and social issues which he's taken care of by using, that's how he solves his problems or so he things.
I would be asking myself what is differnt now other then a restraining order.
What can I really expect to happen to my life and the life of my children if I drop this and allow him to come home with the same old promises of nothing.
Turn your phone off and take a well needed break from all of them especialy MIL right now. You can't think straight if she is pressuring you in any way.