@DeeMor The best I can come up with as to why the separate tanks, is some sort of logistical issue (oil levels, sensors).
I suppose it’s possible that he thought that putting the kids in separate tanks would make their discovery less likely.
This would have likely been a mistake, as you basically double the chances of discovery. If you find one body, you find both.
As for his work activity that day, we simply don’t have the specifics there. LE has the answers, we’ll simply have to wait until we have them.