As it turns out, the back fires saved the brothers' home, as well as the homes of several people who rented from them, and potentially an entire neighborhood.
Emergencies can often call for a different set of rules (remember the post-Katrina euthanasia cases?). A little prosecutorial discretion would go a long way, here.
Matt Welch defended "apartheid fire protection" in our January 2008 issue.
MORE: I should add, here, that had the back fire caused damage to others' property, I'd have no problem with holding the brothers financially liable. But there was no criminal intent, here. Their intent was to preserve their property, and that of their neighbors. And they succeeded.