I am hardly a detective, and this may all be way off base but it sounds like a last ditch effort on the part of the patriarch of the family to buy off the criminal in exchange for his family's safety.
Criminal breaks in and takes the family hostage. The quick-thinking father/husband tries to buy-off and convince the criminal that it would be more advantageous to keep the family alive.
In exchange for sparing the family, cash can be delivered to the house by an assistant. The criminal lets the captive use his phone to tell the other housekeeper not to come over and to reach out to an assistant to come up with a cover story to get the cash delivered to the house. This seems like enough to at least buy some time.
Theoretically; this should be enough to give the criminal a good head start, to get far away from the scene of the crime and hopefully be enough incentive to spare the lives of the captives.
Unfortunately; there truly is no honor among thieves so the perp decides to take the cash and tie up all loose ends by killing everyone. Both infuriating and terribly sad.
Yours is the most logical explanation I’ve found. Thanks.