one little decision that could've saved them all

At the beginning, it's only the parents at the house. The mom hears a noise upstairs and wants to leave, dad insists on checking it out. If he'd gone outside with her and called the cops, maybe signs of an intruder would've been found, and/or the neighbor would've been found. Either probably would've had the family get-together canceled in a hurry, and I'm not of the impression that all of them would've been willing to rearrange their schedules for a second attempt overly quickly.

Watching this tonight, may come back to edit.

When the daughter dies, you can see the mom wishing it had been any son.

As much as I enjoy this movie, even the first time I saw it, painfully obvious it's Felix and Zee, just too many little tells. She doesn't want to be overly friendly, since she plans for most of them to die soon. She goes in last and kind of looks around. After Kelly runs, she suggests others try it, in an attempt to make them easier to pick off.

The fact that they bothered planning this is illogical. Because after the parents die, there are four kids the money would go to, and with following the law, one of them is married, so Kelly would've been included as his heir. So that's five. But, Felix, Crispin, and the three killers, that's six. I know there's of course backstabbings and piggybacks and whatnot to take into account, but that's the basic sum of it. So would you really kill your family and increase the amount of people you have to you share the money with just to get a smaller slice of the pie sooner?