Taking someone off the lease against their will

[Stone Teran]

I'm looking for some advice.  Please don't tell me to consult a lawyer; that's why I'm asking it here.

A mother and her 2 children signed a lease.  2 years later, the mom died.  The boy was 17 and the girl was 16.  The boy just turned 18 and hates his sister.  I believe the girl moved out but I'm not 100% sure.  He wants her off the lease and thinks he has the right because he's over 18 and she's not.  Their aunt now has legal custody of the girl.  Can I take her off the lease without her signature or would I be violating her tenant rights?