Nola Dewester, 69, said the three were siblings and had been caring for their ailing father, who had died in recent months.
The three had frequent run-ins with neighbors, Dewester said.
Several weapons were found in the home, including 12 rifles, 10 handguns and thousands of rounds of ammunition.
The home had recently gone into foreclosure, and the siblings were trying to figure out a way to keep the house, according to Dewester.
The victims, two women and one man, were middle-aged and had gunshot wounds to the upper body.
Investigators are unsure if they were shot before the blaze, or struck after rounds went off during the fire.