Kids go through periods where sleep is hard to come by from time to time.
I would suggest taking a few steps with him.
First. Does he have a routine for bed-time still? They still need a calming ritual. My own daughter is allowed to read to herself for about twenty minutes and then she has to turn the light out to try sleeping.
- Ask him what he thinks is up with the not sleeping thing when it is daylight and just you can talk. Do this when you have time to sit and listen. He very likely doesn't really know what is up and is playing at night because he is bored since he can't sleep. Allow him some time to think through things. You may need to sit silently waiting for answers to questions like, "why do you think you aren't able to sleep."
- You might need to give him some time. As you allow this time for thought and are quietly listening, if there is something he is anxious about, you are demonstrating that you aren't mad and just want to help and building trust. He will come around.
- Point out that his current way of dealing with being awake at night is preventing everyone else from getting sleep and how unfair that is. State this using an "I" such as, "I'm worried none of you are getting enough sleep, but it is especially unfair to your brothers who could be." Then follow your statement with what you would like without giving an answer, "Is there a way you could do something that would be calm and more likely to help you get back to sleep sooner as well as allow your brothers to continue to sleep even though you are awake?" Perhaps he would like a book light and some books to read. Perhaps he could have some headphones and some calming music to listen to. Who knows what he'll offer up. Listen to it.
- Leave the conversation not having made any decisions. "Lets continue to think about this and brainstorm and then we'll talk about it again same time tomorrow and make some decisions about what to do." He might think of something else while you are all "away from it" to add to the conversation because he will feel less pressure when not engaged in the conversation in the moment. You can use the time to consider options he brought up and options you've considered and what you think is a realistic solution and what won't work.
- When you meet again, let him speak first. After you've heard anything else he has to add propose your plan - that hopefully uses elements of what he has said. Put the plan into action and see if it helps. Give the plan at least a week. If it isn't working, revisit and start again.
FYI Sometimes there can be a shift in hormones (they aren't only for adolescence), a growth spurt, a spurt in learning that causes his brain to be over-stimulated so it has a hard time down-shifting at night, shifting adult teeth as they get ready to push baby teeth out of the way, or even a change in his stress level that is subtle and not easily detected even by him but cause temporary bouts of insomnia. Less sleep isn't necessarily a problem for him depending on the route cause (which none of you may ever know).
If he is still functioning fine the rest of the day, he may not need the sleep right now. As long as he isn't keeping the rest of the house up, you are probably better off coming up with ideas with him for options for how to spend those awake hours in the middle of the night. Of course his options should be quiet and not bother others, but also be soothing and the kind that are likely to allow his brain to calm down and let him sleep too. Punishing him is likely to leave him in a lose-lose situation where he is stressed out because he knows he is supposed to be sleeping but can't and is bored out of his mind because it is dark and he is supposed to be quiet but he is wide awake and can't do anything about it.
Some Ideas on Dealing with his waking of others:
Ideas for a "consequence" for waking the others if that aspect of it continues to be a problem even after all of the above steps:
Perhaps he misses out on something cool (a play-date with a friend for example) so he can to do some chores that other members of the house would normally do to allow his family members to "catch up on sleep" that has been missed because of his loudness and activity at night. Whatever you decide to do in this regard, I suggest making sure it is purely a consequence for having awaken every one else, and not for not sleeping.
If you want to go with a sillier idea, but one that will probably be well remembered into his adulthood, I suggest [Mrs. Piggle Wiggle]. Have you tried letting him stay up all night for a night or two? I know it isn't the healthiest thing in the short run, but what if he is allowed to build with legos, read, etc. in the family room - no TV, nothing loud. Then, when everyone else has been allowed to sleep and yet he feels horrible, you can ask him if he knows why he isn't getting along with his friends and brothers anymore. You can ask him if he can figure out why he feels awful and then swoop in as the heroes that really do know what is best for him that create the rules in order to help him stay healthy?
You might even read the Piggle Wiggle books together. Actually, I found a hulu clip that shows the ["Never go to Bedders Cure"] on a television show that depicts Mrs. Piggle Wiggle. (I had no idea they'd put this classic on film!!). It doesn't follow the book to a tee, but you'll get the idea anyway. The actual "Never Want to Go to Bedder's Cure is in the first book, "Mrs. Piggle Wiggle.