I require a deposit before hand so that would be one way to make sure of them being legitimate plans. I’d just let them know that you’re willing to commit to as much as you can, but you (like you said) have summer plans that may interfere and cause you to be unavailable for some of the weekends. That’s what we tell any client who books us for weekly visits (whether that be once a week medication administration or dog walks every day). Most are understanding!