IMO young kids sleep thru everything at this time of night ( morning).
I am assuming for this scenario, that perhaps the two girls bunked together in the same room, with the baby in the crib and the 4 yr old in the big girl bed, maybe with the dog. Their door closed with probably a monitor inside. They all heard nothing.
We know so little. It well could be random. Someone mentioned maybe the rear door was left ajar inadvertently after they let the dog out. Someone walks by and sees an opportunity.
Why would someone/a robber go into an occupied house? Happens all the time.
They could have gone in and been “ casing the place” thought it was an easy grab the purse in the kitchen etc, when the husband heard something. He tells the wife to stay put while he checks things out. He goes down - locks eyes with the robber - runs back upstairs - robber runs after him shoots him at the side of the bed and shoots the wife who is in bed.
Robber freaks out and takes off bc he never intended for that to happen. Spur of the moment eff up and gets out.
obvi it could be any number of things.
I am mindful that the holiday season makes even stable people unstable. Lots of drinking drugging and people just generally. strung out. Economic pressure and exhaustion with trying to make ends meet, people do desperate things
JMO