It all depends on the causes of all three fires. Maybe the first was caused by say a gas leak through no fault of the owners/renters. The second house gets struck by lightning and burns. The third time someone passes out while smoking in bed. All unrelated and just shitty luck.
This is why fires are investigated.
Here’s some interesting info. I never heard the stories about the son. Guilty?
Probably not coincidence, but 2 possible related facts: 1) firemen/arson investigators aren’t stupid and 2) juvenile records are sealed for a reason.