I'm Lucy, and I'd be happy to answer your questions today.
No, you're not wrong. If Rich is not a party to the lease (and it sounds like he isn't), the money he gave you is a $600 gift to his son. That transaction is between them and has nothing to do with you. Pennsylvania law requires that, when a tenant moves, the security deposit be returned to the tenant - not to a third party. If you actually DID give the money to Rich at the end of the lease, Rob could sue you for violation of the security deposit statutes, because Rob is the tenant and he is entitled to a refund. You cannot be forced to become a party to a transaction you didn't know about when it was made.
Also, if you're still living with Rob, he (and by extension, his father) would never have the right to demand his security deposit back. It's OK to agree to use it toward rent, but a tenant can't just arbitrarily insist on getting their deposit back before they've moved out.
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