PRIORITY ONE is get your cats inside...as others have stated; this dog WILL kill them, given the opportunity. Check with local ordinances...if there is a leash law, and the neighbors don’t obey it; call the cops. Don’t let your cats out UNTIL these people learn to restrain the animal, preferably in a pen. Some towns even have outright BANS against pit bulls and other dangerous breeds. Talk to the police and find out what you can do within the letter of the law.
I’m more worried about RR’s mom, no?