Stands,
The others are right. You need to lock your difficult child out. Refuse to let him back in. He needs to stand on his own two feet. You owe it to your easy child to keep him safe from harm. And that means safe from his brother stealing his things that he worked so hard for. If he can't be safe in his own home, where can your easy child be safe?
Here's something to think about...my difficult child (17 3/4) is having a terrible time right now with rages and meltdowns and uncontrollable behaviour. Because he can't function on his own, we are going to place him in an Residential Treatment Center (RTC). Until we can get the Residential Treatment Center (RTC) placement finalized, we have sent our easy child to live with relatives, so that he can be safe from harm.
It breaks my heart that my baby isn't home with us, but we know he's safe, loved, well cared for, and not in danger of mistreatment at the hands of our difficult child.
My little one is 5, yours is 17, but it's the same situation. You need to do whatever you have to in order to protect your easy child. Your difficult child is old enough to make or break on his own, and he will continue to manipulate you and make your easy child's life awful until you force him.
I would also recommend that you and your easy child get therapy to deal with all of the feelings that you are dealing with. It's hard. It's extreme parenting. But you can do it.
Trinity.