Show him you mean business. Tell him to get into bed even if you have to sound really tough about it. Keep the lights off and tell  him you'll come get him when it's time to get up. If he doesn't cooperate, tell him his other choice is that you will take him to your basement and he can play there by himself with the door shut (or some other equally bad idea). He'll pick up on your serious attitude if you can be very very firm in the way you talk to him.

He's old enough to understand punishment. If he wakes up his brother take away something from him that will really upset him. Maybe there will be a few bad nights with lots of crying and everyone awake, but after that everyone will sleep for the next year, so it's worth it!

Invite him into your room to sleep on a mattress on the floor. Maybe he just wants company.