If the police can prove he knew the gun was stolen, then even though the statute of limitations may have run on the theft he could still be charged with criminal possession of stolen property, because he possessed it up until the time he sold it to pawn shop owner, so that statute of limitations is good up until the day he sold it (I'd guess I know nothing about Texas law).
Would this guy fall for you showing up with the one gun you have and telling him, listen Joe, the cops brought this back, you and I both know what's up but Gramma's heart would break if we had you arrested, so just give me back the other five guns and we'll keep this between us?
Of course I would have a tape recorder with me and then let the cops have him as soon as he fessed up and gave me the other guns-worthless turd, if this is how he treats his family, imagine the evil this guy spreads over perfect strangers.