Again, an early source. This also confirms, IMO, that the girls likely died of smoke inhalation, as the fire maybe didn't even reach the top floor?
Former Jefferson City girl one of four sisters killed in Indiana house-fire
The Indiana State Fire Marshal said the cause of the fire is undetermined due to the amount of damage. The fire originated in the kitchen area, possibly behind the refrigerator. (Again, this is an early article, before the arson and stove statements)
The home where the fire started has two apartments, one upstairs and one downstairs. The fire was concentrated on the lower level and firefighters said the second floor apartments didn’t sustain any damage.