LE has not said DM and BF were in the same bed, they could have been, or they could have been on the 1st (BF) and 2nd (DM) floors.
Regardless, IMO, either or both of them could have used the 2nd floor bathroom earlier that morning without noticing anything unusual if it was early (maybe not fully light out) and/or they were groggy, because the bathroom and 2 bedrooms on the second floor seem to be all "around the corner" and not in plain view of eachother, for privacy reasons in the layout, I'm assuming.
The PCA says Xana's and Ethan's bodies were in her bedroom, which they might not have even thought of looking "into" if they went to the toilet and then back to bed in the dark or before full daylight on a Sunday morning after a late night.
They thought their housemates were sleeping in like they were, since they were all up well past midnight, and Xana had her boyfriend over spending the night, which would make them even less likely to walk up to her bedroom door that morning and inspect their status, IMO.
We don't know if Xana's bedroom door was closed, or if there was blood that was obvious outside her bedroom door on the 2nd floor at casual glance.
I think it wasn't until late into the morning going on noon that DM and BF really woke up and reality came crashing down when they came into the kitchen and saw some blood and one of them on the floor when they looked into Xana's room. Prior to that, I think they tried to contact their housemates on their cell phones about the noises of the night before and and maybe the "masked man" DM saw, and they weren't answering, so they assumed everything was okay and they went back to bed to give their hosuemates who were up until 3 or 4 am time to sleep in.
IIRC, very early on it was in MSM that Ethan had plans with his brother at 11:30 am or 12:00 pm on Sunday to go golfing, and when he showed up at the house and no one was answering the door, and he couldn't reach Ethan on his cell phone, and neither he or DM and BF who answered the door could reach them, that that's when DM and BF went upstairs, maybe with his brother.
That was incredibly traumatic, and Kaylee's father said this:
""You got to remember these two girls were so upset that when they went outside after seeing this ... one passed out," he said. "And the other one was so hyperventilating that the message wasn’t clear enough for the operator.""
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