ugh - i dont have too much advice, just wanted to sympathize lol, because i had this trouble with my boy who is now 6, he didnt sleep a full night till he was five, he just didnt need a lot of sleep, and still doesnt.
it works better for him if i get him up early in the morning, around 7 or so, then he is usually in bed by 9, but he is still awake at 11 almost always, reading under his covers!
he used to come into my room almost every night, and the way i got around him waking me was i set him a pallet up on the floor, and he could come in and lie on it in the night, as long as he didnt wake us up, he did that everynight for around a year!, i didnt mind that so much as he tried his best not to wake us up.
my son fights me every night to go to bed - i think some children are programmed to do this, no matter what "rountines" we set up for them.
i used to share a room with my sister and remember doing the exact same thing you describe, and my mother shouting up the stairs "im going to separate you 2" lol.
maybe you could seperate them, or tell them they are not under any circumstances allowed to leave their own beds - they can talk quietly to each other or look at a book, but no throwing, jumping etc, if they leave their beds they get spanked/confiscations/time out/add your punishment etc.
my son just could not go to sleep at 8pm, not ever, even when he was a baby.
hope you get some better advice than i have given