Just sit him down and make him understand the committment he made when he got them.
Then have him help you find them a new home. Maybe someone on here could take them were are you located.

If he has loss interest you can't make him refind the interest. But having him help find a new home would let him follow through and both of you would feel better about were they were going.

All we have is rescues, so I know other would take them in also. Best Peeperkeeper