My name and another on the lease, they moved their 18yo into our home, but when the other person who name on the lease moved out their child did not go with them and still there, not paying rent or anything.
Generally, NO. Only the LL can evict. You will need to speak with LL, though its possible the LL will evict BOTH of you if the lease does not allow people to move in other tenants without written approval from LL, for the exact reason you are confronted with.
Real Estate Attorney
Assuming the person was originally a "guest" and was never a "tenant," you might be able to bring an action to have the person removed. I recommend discussing the full details with an experienced landlord/tenant attorney.l
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