One of the 'advantages' of being older is exhaustion. Yes my 9yo DGD has always stayed up quite late here (9.30?), but we tend to go to bed within half an hour of each other. The hall light is on until I go to bed, and when I go in then, she's always asleep.
As a teacher, imo when your DGC say 'No!', they're pushing boundaries. You let them get away with it now, you will pay. And you have 3? All at the same time? Wow. I'm a 'grannie's house, grannie's rules'. I'd drop subtle hints that maybe next time only the younger 2 stay. They're getting older and so are you - it's supposed to be a pleasure having them stay!