Certain answers would help a lot in trying to figure out how things played out.
What hours were dad's work shift? I have found mention of night shift at Jennie Os being till 1am, so did dad unexpectedly come home early? Did perps know his normal routine, and know that it would only be mum and Jayme at home earlier in the evening? But then did dad maybe feel ill and knocked off work earlier than expected. Maybe perps left breaking into house until say around midnight, thinking Jayme and mum would both be asleep by then, less traffic going past, neighbours asleep as well. They probably thought an hour was plenty of time for their purposes, but then dad came home early?
Were the shots that the neighbour heard (around 12.31) when dad arrived at the house, and the shots were heard because the door was open?
Was the door kicked in at (say in my theory) just after midnight, as the perp was going for a blitz attack, bursting into the house, and thinking mum and daughter would be groggy/still half asleep and not realise what was going on straight away?
Was it a sole perp or was there more than one? I'm thinking if dad was first victim shot, and mum and Jayme are hiding in bathroom ... it has been reported there was a lot of shouting or yelling could be heard in the 911 call, which makes me wonder if there may have been more than one perp?
The timing between sound of shots and 911 call - the arrival and shooting of dad wasn't in the original plan, the perp or perps has to now change tactic because they have murdered somebody. Maybe if more than one perp they even argued over what to do. Maybe one wanted to flee immediately, maybe the other said that we have to kill them (mum and Jayme) because they either know their ids or could at least provide a good description of them to police. Maybe they were yelling at mum to open bathroom door, and depending on whether Jayme and mum were together in there or not, if Jayme had hidden somewhere else and they found her, mum would have then obeyed whatever orders they gave her, including opening bathroom door. They end up killing mum. But for whatever reason, whether Jayme was the original target of somebody obsessed with her, or they can't bring themselves to kill a kid, or they figure take her as a hostage to try and protect them from LE (leverage - back off or we kill her) , they then take Jayme with them.
The getaway - they realise LE will be coming (from direction of town), so they flee by going the opposite direction (west), even without speeding, they will be long gone by the time LE reach the house, and even further away by the time LE ascertain was has happened.