Advice...anyone?

I am rapidly approaching my wits' end with my kids when it comes to going to bed. In fact, this post is pretty much proof that I'm there. Here's the situation:

We are renting a 4 bedroom house, 1 is the Master bedroom, 1 is the kids' bedroom, 1 is a guest room and the 4th (the only one downstairs) has all of our workout equipment in it and is pretty much used daily. When Hakan was born he slept in our room until he was waking up less frequently to eat, then he and Pyper shared a room. This worked fine. Then we moved into our own house and they each got their own room. This worked fine, too. Then we moved here and put them back in together to free up one of the bedrooms. It worked fine for a while, but for the past several weeks it has been a battle almost every time they go down for a nap or for the night. Honestly, it's Hakan. He just will not be quiet and just go to sleep. He gets up and plays and messes with Pyper and acts silly and just makes a ruckus. Pyper sometimes participates, but she usually gets annoyed with him and comes out to tell us what he's doing.

Originally we had their room set up with the beds on the far wall from the door, one in each corner with a low bookcase separating them. Pyper's bed was by the window, but I eventually realized that her bed was on top of the vent so their room was never very well heated. With summer coming on and the eventual need for A/C, I decided to switch their beds and put Hakan's over the vent because there's much more room underneath for the air to flow. Big mistake. Hakan would constantly mess with the blinds, look out the window, pound on the window, etc. The other night I finally got fed up and totally rearranged their room. Their beds are further apart now and no one is by the window. I like the arrangement, but this doesn't seem to have helped the whole playing around at bedtime issue. They're actually in there right now and I hear something banging, even though I've been in there twice and have yelled at him to be quiet multiple times since I laid them down ten minutes ago. Aaaand... here comes Pyper...

Is there any way to resolve this?? Yes, we're seriously considering putting them in seperate rooms again, but it's a tough decision. Pyper doesn't like sleeping alone, and I think it's good for them to share a room. It gives them some added closeness as brother and sister, plus comfort and security at night. It would also mean either putting Pyper in the room downstairs (all by herself) and giving up the workout room, or moving the guest room into the room downstairs where the furniture doesn't fit very well. Aarrrgghh!!!

I'm just so tired of fighting with them (read: Hakan) every dang day and night. 2/3 of the time we end up just yanking one of them (usually Pyper) out and putting them in the guest room or our room to fall asleep. What's their deal??? Some nights it takes literally hours for them to finally go to sleep. You have no idea how tired I am of saying, "Be quiet and go to sleep," "Don't get up," "Stop messing around," "Do you need a spank?" "Just go to sleep!" I'm even more tired of getting angry and usually losing my temper. It so, so sucks. At least at night Aaron can field some of it, so if I start losing my cool he can take over. But honestly, this just can't go on.

So, the point of this long-winded post is to beg and plead for help. Does anyone have any suggestions on what we could do? Please, anything. Even if you just want to weigh in on the whole "to seperate vs. not to seperate" quandry, I really, really need some feedback here.

Holy crap, is it actually quiet in there??