It sounds like they know the game of turning the pet into an ESA. You won't win this. However, inspections should never be done virtually because you can't smell odors. If they just sprayed air freshener so you can's smell anything, tell them you'll have to do another inspection because of that. I once had an apartment that the tenant cleaned perfectly, except for the threshold that was still covered in dog crap; I thought I had painted it brown - nope! The odor was so bad I don't know how anybody could live there! The dog urine got into the sub-floor and they were smoking.
What I would do is make sure that's not happening to your property. If they're responsible pet owners (with the dog running loose, probably not) than you'll be fine. As for the radon, check your state law to see what's required of you. If they are destroying the house, I wouldn't put any new equipment in because they'll destroy that too. You can evict them for damage, but not for having the dogs. Take pictures and if you need to, cut out a piece of the carpet that's soaked in urine to take to court with you.
I've been sharing a bad scenario, but hopefully they're fine and will rent from you a very long time, happily paying rent increases because they'll have a hard time finding a new place with their dogs.