I'd ask about house rules, whether the kids are generally good about abiding by them, and what to do if they don't.

Friends allowed over? If so, when, how many? Can they spend the night? Curfews?

I wouldn't agree unless kids had to be home at a certain time and no friends over.

They will probably want you to leave them alone most of the time

If the kids ask to drive, are you to say yes? How many kids can be in the house at once? Consider that if each invites two or three, that's 9-12 kids at once.

Will you be cooking dinners for them? Will there be a curfew?

A friend of a good family friend is looking for someone to stay with their three teenagers for 4 days. I've nannied/housesat for 7 years but the kids are always under 10. I haven't talked to him yet, but from what I understand he just needs someone to be there at night and drive them to school. What do I need to ask before agreeing to staying with 2 16 year olds and a 17 year old for 4 days? Any advice?