Then KEEP them. Once they are out of your hands you have zero control over who owns them, if they are rehomed again and again or split up and what kind of care they receive. Older male cats are about the most unadoptable you can get in the shelter world and asking someone to take both is a long shot. Please microchip and leave your name as backup in case they are turned into a shelter down the line. Also, most shelters won't take owner surrenders as they are up to their eyeballs in cats already so you will have to find them a home yourself.