You can always ask them, just make sure they know the deal and see what they think is fair. They might be willing to do it for not much just because they like you, and coming in real high might make them feel like they're obligated to do more than you're actually asking.
If it's literally just "we want someone in the house in case they fall, and to keep eyes on when they're doing something dangerous/occasionally flip breakers" that's definitely something most people would do for beer money/dinner/IOU especially if they had no other plans.
Coming in with a big hourly offer can definitely make someone feel weird depending on the work and their relationship with you, but that's between you and them.