Desperate attempt to “protect” the empire. The son’s boat accident was too big to sweep under the rug, and a whole bunch of stuff probably would have come out if that went to trial. And the wife was rumored to be seeking divorce, the forensic accounting that goes with big money divorces can unravel a lot of secrets.
So he shot them to shut them up? Plausible. Wonder what happened to the boat wreck trial? Pau Pau’s death wouldn’t have stopped a civil suit.