I think a likely scenario is that some one knocked, dad went to door, looked out and would not open the door for the suspect. He kicked in the door, shot dad. Mom barricaded herself and daughter in bathroom. Suspect found them, shot mom, took Jayme.
If you witnessed your mom being killed and saw your dad was killed also, it wouldn't be difficult to get you to be quiet, get in a car and leave the area.
They probably took the chair for ballistic evidence, there is probably a bullet lodged in it somewhere and they took it to the lab to have it removed without damaging it, for comparison, to determine what caliber, model, type of ammo, etc.
I do think Jayme was the target. I do not think they're was a debt involved. No chance in recouping your money if the warmers are feed.