The toilet is your responsibility to fix as the landlord. I'm not sure about the rusty tub - that sounds like something you can take care of when you renovate the unit. You can charge them to fix the AC if the dog really did it.
You can certainly have the city inspector get involved if they are actually running a business out of the house, but probably the result will be that you'll get in trouble as the property owner, rather than them.
As others have mentioned, you accepted them and their dogs as tenants when you bought the home with them in place.
You should have a conversation with them thusly:
1) Only one dog is allowed per your lease
2) you have two dogs
3) here's an addendum that legalizes your second dog
4) But please note that you can't breed dogs here or have more dogs (write it straight into the addendum)
5) If you start breeding dogs, I will do a quit or cure notice, which leads to eviction, and I'll get the city inspector involved (you'll get the city inspector involved so you can show actual damages to the judge)
This is why I don't allow dogs in my places. Not because I don't like dogs - I do - but I've observed WAY too many people aren't good dog owners. As an aside - it's a good idea to be nice to your local town officials (city inspectors, etc) because they can help you out or hurt you depending on how they feel about you. I deal with these men and ladies all the time (as part of my job) and most of the public treats them poorly, so a bit of friendliness goes a long way.