Grace–HUGE kudos to you. I am running very late, but will type fast.
(For those who missed the comment, she’s taking in refugee dogs.)
I would avoid cross-contamination of your yard; I know your guys are all adults but even so there are some nasty bugs that stranger dogs bring in and you don’t have a lot of control over them because they’re not yours. So hand-walk the newbies at least until you see some stool and know that they’re relatively healthy.
I’d get Capstar if you can; super gentle and effective. Cap each newbie and quarantine for half an hour until all fleas are dead.
Other than that, it’s baby gates and crates and careful rotation. If you decide to have them meet your dogs, do so outside where everyone can get away from one another. Remember that even if they’re getting along well outside, the emotionally charged areas of the house (small rooms, bedrooms, doorways, stairs, anywhere involving food) are prone to conflict. Don’t let them get in a doorway together; don’t feed together. Don’t let them be in the kitchen together if anyone is cooking or eating.
You’re almost certainly going to be just fine–most dogs do very well in these kind of situations. Just be a defensive driver (in other words, assume that dog X WILL start something, not that he won’t) and give everybody a smooch for me.
I am heading out in the morning for Hershey PA, which is the location of Groom Expo and Animal Behavior Conference, the largest dog-a-palooza within 20 hours of me. I’ll be gone until Monday, though if there’s WiFi in the hotel I’ll post pictures of dogs groomed like chickens if at all possible. I’ll be glomming samples and taking some master classes (ha! Hope they don’t throw me out) and coming home full of stories and pictures.