The neighbor does need to watch out for his cats. But (soap-box alert) the cats shouldn't be outside anyway as cats (even well-fed ones) kill millions of birds, voles, and other native wildlife each year (not to mention that cats that stay indoors tend to live longer). As long as people give the foxes space, there aren't health or safety risks to people. The foxes will only stick around till the end of summer and then the kits will head out to find new territories. You'll be able to fill in the den site when they are done. The only thing you need to do now is just pick up the foxes' "leftovers" if they bother you. They tend to be pretty messy around the den site. Try to clean up while they aren't around. What you pick up can go in the garbage. If you have other questions, please let me know.