Whether the uncle lives in PA or not, a FFL (licensed dealer) will be needed to lawfully transfer the guns to your wife.

There should be no problem keeping the firearms in your home, provided they are secured in a manner which prevents you from accessing them in any way. They should be secured with a lock which you do not possess a key to, or in a safe which you do not have the combination to.

While your sons can legally use the firearms, (with or without supervision depending on the circumstances), they cannot maintain full and unlimited custody and control of the rifles until they turn 18.