You should definitely contact the property owner. Sometimes you can hold a property owner liable for things at their property that they didn’t know about, but it’s a lot easier if you can prove they knew. And of course, where pit bull attacks are concerned, winning a liability judgement in court is not generally what you really want — what you want is to prevent an attack from ever happening. It’s entirely possible that these renters’ lease prohibits them from having these dogs at the property. Do be careful, though, because the renters may figure out (or be told) that it was you who notified the property owner, and there’s certainly a risk of retaliation.
Thanks for the reply.