The civil suit awards will probably be epic. Vacationing with terminally ill father, the two daughters both die. Assuming the mom is still in the picture she’s going to get a LOT of sympathy from a jury. The owners might not get jail time but they will be living out of a cardboard box when it’s over, I bet.
The rental house is destroyed. Because their negligence caused the fire, their insurance policy is void. Assuming there was a mortgage, the bank now owns the land.
They might have other real estate, but how much of that is mortgaged?
They'll probably be bankrupted by any lawsuit, and the mother will only collect a small portion of any epic award.