Jeff's mother had died from cancer, and the stepmother had also lost her husband around the same time. I believe it was a year or two before the new couple married. From what I understand Jeff wasn't fond of her. I think his dad wanted him to call his stepmother "mom" and I think that was too soon if ever for that.
Jeff did have a record for breaking in houses down the road, also a fact not well known is that another home on that road was robbed the weekend before the murders, a shotgun was taken.
The area is rural and gun blasts are very common, so maybe no one noticed. Plus most of the killing was done in the basement, keeping the sound inside. Only the dad was upstairs. The home is very visible from the road, right next to the small church. Easy to see if cars are outside or curtains closed, ect.
No one really knows the reason the family left Florida so suddenly, but there was talk of money laundering. Some of the Florida family friends had some questionable dealings talked about in the book.