Some people gave you great advise!
I would like to add that just this week a similar case was on Judge Jeanine Pirro and maybe you can even google that episode. The owners were suid for $ 5,000.- since it is small claims court.
The owners won the case! They had a inspector come out to test the house and the official test came back similar to yours. The tenants had medical bills and claimed it was all due to the mold and the house made them sick.
In your case: Perhaps they have a matrass with bed bugs or other bacteria that makes them sick. If your test came back the way it did, you have nothing to worry, and IMO you don't need to make all legal costs. As long as you have the official report and I would go and do an inspection at the home and video tape everything and make pictures of it. In my State it is allowed, I did it once when I didn't trust my tenants and I was right, they vanished shortly after. They started claiming I didn't had ask them to give consent to be taped (I had a tape recorder on as well in case the video sound wouldn't be good enough)...They clearly stated they gave consent but even without it you have the right to tape your own home from the inside and you need proof also to protect your self so they can't claim you took anything. You need another person to go in with you so one will point out everything and the other is taping. If they don't give consent to be taped you have to leave their image out but you can tape you property from the inside. I would clearly look how clean it is, which is their responsibility and look what state their furniture is in and see if they smoke inside the home...
I hope you also have pictures of the inside before they moved in so it will show how clean it was before they moved in...if so you should be fine!