Right, one or 2 quick strikes in the area of the chest or throat as the local coroner first reported with a lethal weapon made for killing to a sleeping Maddie and barely awake Kaylee. They were killed and left bleeding out in their bed in a relatively contained area IMO.The massive bloody crime scene that LE found at noon the next day was after the victims had bleed out.
It was reported early on that Xana had defensive wounds to her hands IIRC? I don't think we can definitively rule out that Xana and Ethan
might have been killed first at this point. We know that Xana was awake and on TIKTOK and had received a DD order. It's the sheath left by Maddie that throws me off the idea.
If Xana and Ethan were killed first, that could account for the blood on the stair railing and the mixed DNA if Bryan touched the rail with a gloved hand. If male DNA was identified it could have been Ethan's mixed with Xana's.
Just hypothesizing, need more coffee.

We have learned a few new things since the Motions have been released such as DM going down to BF's room to sleep. Who knows?
JMO