Sleep is overrated

Artist has decided he's a frat boy in training. Even if I get him to sleep at a reasonable hour, he gets back up sometime between midnight and one, and stays up until four or five. Even worse, he wants to be downstairs, and if we try to keep him in his room or ours, he throws a tantrum that wakes his brothers, so we have THREE cranky boys up in the middle of the night. He does this no matter how much or little sleep we allow him to have during the day, whether he gets up early or sleeps in late, whether we've had an action packed day or a laid back day. I am exhausted, John's having trouble sleeping even without the demon-like screeching in the middle of the night, and the wear is even starting to show on the other two boys, though you'd never know it with Fighter's continued desire to greet the sun with a smile as soon as possible after it appears. I know that conventional wisdom says a child begins to have difficulties sleeping just as they're about to have a major advancement (in Artist's case, I'm hoping for a language explosion) but I honestly don't know how much more of this our family can bear!