Nachum,
If the girls were at boarding school, that means the one child was the boy.
The three adults could have been any combination of the 2 housekeepers, the CEO, and his wife.
Did his wife work?
Did he show up for work?
Any friction between the CEO’s company and a prominent person?
We only know that he worked on some significant projects for the government and (at this point) arson is suspected.
Spouses of the help also. An interesting who-done-it.