Not being that familiar, reading into this situation is like a Agatha Christie book with a lot of red herrings.
Ron DeFeo, Jr. said the mother killed everyone then changed his story that the sister Dawn killed everyone.
There were multiple friends involved.
With the victims, there was no struggle, no drugs in their body, no silencer on the rifle, no noise reported by the neighbors, and all the victims according to wikipedia were found stretched out face down in their beds.
But Ron was bad on LSD and heroin which fried his brain.
And as mentioned horrible physical and mental abuse by the father with all the family and family members against family members, which is probably the reason Ron killed everyone.
But this haunted house could had driven every crazy !
I think the house was haunted.