I think she was the first one to be killed. Logic - he planned to do it for a while, and was just waiting for a good moment. But if he failed to kill her that night, absence of girls would be hard to explain to her. So SW had to go first. The delayed flight might have been a bonus, as she was tired and let her guards down. I think that he either killed her close to the purse - if caressing her neck was his habit, she was caught unaware, or upstairs.
The kids were killed when sleeping. He had already passed that line. It was easier. The dog howled when one of them was killed.
Whether the AP heard something, like complaints, or “sometimes I hope something happens to her”, or something else, I don’t know. Online I saw the screenshot with the AP’s name but it might be less relevant as if not one, there might have been another.
He had the night to clean. But there still might have been some smell. In the morning, he got rid of the bodies.