Can't you kick them out at 16?  We did it with our daughter when she got way out of hand.  She did smarten up and come back after a month or two, but if it was P I was dealing with it would not have happened

I know there is a law that says that you are financially responsible for them until 18, but there is a way around that law...

I just told them that yes, we have a room and food and everything available, but the child has to follow the rules and have respect for me to give it to them.  They are more than welcome to come home if they follow the rules.  Once I explained the behaviors we were off the hook with the financials thing...

As long as these kids are "welcome" home anytime *they* are ready to follow rules then it is okay.