He has rights, he served his time. In our current system there just isn't much that can be done. If I were in charge I can gaurantee you he wouldn't be living across the street from anyone, he would be one of those "career prisoners" instead of a "career criminal".
RIP, unless your state has a law about "childrens welfare" where they will force a sex offender to move if he lives a certain distance from a school or daycare etc. your probably stuck with him (that point being, start a daycare in your home, & they'll have to force him to move).
My advice would be to get a lawyer, you can sue anyone over anything. Just get a lawyer & start slinging paper at him & the people he's staying with. It'll cost them so much money to defend themselves they will probably get him to move, but then he'll probably be pissed at you if he isn't already...got any security cameras & locking gas caps?
You see where I'm going with this, you'll have to find a way to work the system to drive him out legally.