C.A.
My kids don't share a room regularly but sometimes 'sleepover' together. I use this method when friends sleepover as well. After the lights are out, I allow 10 minutes of 'talk-time'. It's supposed to be quiet voices and staying in the bed. Then I come back and say it's now time to sleep. I find the permission to talk for a while diffuses the lights out issue.
I sometimes use the 'losing privileges' as well when they are delaying going to bed. It's usually something they wanted to do or have the next day.