Polite blackmail?

So being a first time host family isn’t for the weak. Our kids have it easy and the only rule they have is to keep their room clean. There is an option at their school to be camp counselors for one school week. Basically we’re forcing them to do it because my spouse and I are on the verge of a nervous breakdown. They both immediately agreed which was surprising because one of them thinks they’re slick and always comes up with the weakest excuses when confronted about minor issues in the past. Last night, they came to us groveling and backpedaling with very lame excuses that we almost laughed in their faces about. Yes we need that damn week to ourselves but also, being a camp counselor as a foreign teenager would mean a lot to these middle schoolers and give them leadership experience. We don’t plan on telling the kids that they’re stressing us out and we need a break but we did consider mentioning that all of our elaborate/expensive daytrips and activities will stop. We did say that we were requiring them to participate UNLESS they had a legit excuse and one was not provided.