K.S.
I would say they should start getting ready for bed around 7 or 7:30 to be in bed by 8 at the latest (esp for the younger one.) Maybe in bed by 7:30 for the youngest, 7:45 for the oldest. If they're in different rooms. If they stay in bed or not can't really be helped, but enforce that once put in bed (bath done, potty done, teeth brushed and story read), it's bedtime, they're not coming out of the room.
It'll take a while, but once they understand that it's bedtime for them and mommy won't give them attention.. They'll get bored complaining and go to sleep. Removing toys (esp. ones that make noise) would also help with the it's bed time, not playtime. idea.