Were they murdered? No
Were their deaths an accident? Yes
Does the fire have anything to do with their deaths? Related, but they did not die because of the fire
You said the cabin was not standing when they were found, but they were found in the cabin. Were they found under cabin rubble? They were found in the cabin rubble
If so, was the the cabin collapsing the cause of their deaths? Related, but they did not die directly from the cabin collapsing
Were they happy when they died? Doubt it.