Per the question about why he took all four but killed two, there are many possibilities. It indicates to me that all four of the victims voluntarily left the home or were taken out of the home at gunpoint. If they voluntarily left, they might have met him along a road, where he might have waited under the false pretense that his car had stalled. They also might have driven him home. Since the girls were with mom, we can presume that the time for something like that to have occurred would have been in the morning after the girls were dressed and they were on their way to school. If he decided to take all four at gunpoint, he either thought that the mother would go along with his plan or had to take her so that she could not tell the father.