What to tell families when multiple dogs are booked?

I have a booking for the upcoming weekend with 2 dogs. I have met them and they seem like they have a good temperament and got along famously with my own dog. The dog we watched last weekend, also a great temperament and had absolutely no issues with her, requested the same upcoming weekend. I allow up to 3 dogs at a time, but I am wondering how (or even IF) I communicate the two families about the multiple booking. Thanks!