Many leases, if you read them, say "no cats or dogs" and having the ratties might be okay. I'd just be up front, but say "small animals" or "little furries, they're always in their cage" as some people are biased against the word "rats" and don't know they can be great pets. Also, if a lease says "no fish tanks," you can say "would the tank be okay if it doesn't have water in it?" if you have tanks for part of your rattie's homes, because most landlard's objections are to that quantity of water and the potential for problems that way.

Keep looking, and if you fall in love with a place, you can always ask, even volunteer to bring over your rat for an "interview" if the person seems unsure, so they can charm the future landlord with their cuteness, whiskers and cleanliness.