As much as I hate sleepovers (because of the cranky kid factor), he really doesn't have much say as to how much sleep he gets. Dd9 went on a sleepover at her bff's for the first time, and they stayed up all night long (even though dd and another friend begged to go to sleep). When bff had a slumber birthday party, both dd and the other friend asked to be able to go to the party, and picked up late, and not sleep over.
Dd9 has a friend sleeping over tomorrow night, and they will be told that if they're not sleeping by 11, I will call her gf's mom (whom I'm friends with), to pick her up (we have NYE the next night). Dd14 slept over her gf's house last night, with a bunch of other girls, but if she's tired, she'll just go nap, and not be miserable around me. Ds12 - if he goes to a slumber party, I KNOW he won't get any sleep, because his friends are up all night.
Dd9 has a friend sleeping over tomorrow night, and they will be told that if they're not sleeping by 11, I will call her gf's mom (whom I'm friends with), to pick her up (we have NYE the next night). Dd14 slept over her gf's house last night, with a bunch of other girls, but if she's tired, she'll just go nap, and not be miserable around me. Ds12 - if he goes to a slumber party, I KNOW he won't get any sleep, because his friends are up all night.

We make sure the other parents are onboard and they have been so far.

