Yikes. Like Frances said, having extras of everything is a great idea. It doesn't have to be fancy stuff - I've got a pile of old towels that I can put down as extra bedding if I need to (and they're far easier to wash than dog beds, so if you've got markers, towels may be the way to go). I've got a couple different sized crates as well. One of the rescues in my area takes donations of dog supplies and then sells any extras at a great price. I got one of my wire crates for $20ish? I have a huge stash of toys, and I always ask the owners what type of toys their dog prefers and whether or not they're prone to tearing them up - if they're a hard chewer or stuffy destroyer, I can put away some of the softer toys before the stay so I don't have to worry about them. Another supply I'd recommend are 'blue pads' from a medical supply store. They're like puppy pads, but cheaper. If you're dealing with dogs who are going in the house while you're not there, and you aren't able to crate them, this may be your best chance to keep the house somewhat clean for the stay.
In the future, it might be worth it to create a packing checklist for owners to prepare for the stay to remind them of everything they should bring - food, medication, dog bags, leash, collar/harness, vaccination records, dog bed, crate, toys... whatever is important to you (and the dogs). You'll never be able to get people to bring 100% of the items 100% of the time, but being clear in your expectations goes a long way.
For these particular dogs, if they're marking while you're home, I'd probably go so far as to tether them to you with a lightweight leash or ribbon or whatever you have around. Tethering is a great way to get new dogs who are a bit uncomfortable settled in. They learn boundaries and you're always able to monitor them so good behaviors can be rewarded and bad behaviors can be stopped. When you're really able to give them your full attention, you can let them drag the leads in a safe area. Any accidents, and they lose freedom again. While you're away, I'd confine them somewhere safe, like a bathroom or other area that's easy to clean up. Taking long walks right before you go can help prevent the house pooping, provided you can get them to go on the walk.