If he isn't going to sleep anyways then put his playpen in the room with you and just keep laying him down till he gets it. He should not have his playpen where he can reach anything such as toys. At the same time he really shouldn't be in a playpen either as he is probably nearing the weight limits and certainly if he is not going to lay still so there is danger of tipping it over or breaking it. I would be "screaming" back in my very angry voice to let him know that I have had enough. They are smart and they get it. He is old enough to be bribed too - no rest quietly (keep him down on level you are on) no treat after, etc.

Make sure his parents know about the napping issues and make sure they are letting him cry it out at home. If he is the younger then they may be going to him at the first whimper lest the older brother be woken up. That will need to change.