I believe women, if they have a propensity for evil, are more evil and devious than men and while a good mom or even a good woman would never hurt a child, an evil woman wouldn’t bat an eyelash at killing her own child. I was not there and can’t give you proof but I absolutely believe when Chad let her know they would be happier without her “dark” children, she took it from there, did the planning and killed the kids. Of course, AC had to stand by for disposal. He was also expected to get rid of Brandon, Charles and Tammy. As Lori put it, “the idiot” couldn’t do anything right. Even with the shooting of Charles, I think Alex shot once and she finished Charles off.
Even after all the gun range practices, he shot at Tammy and missed her, shot at Brandon and missed him. I believe Chad killed Tammy and just wanted Alex as a standby.
I also believe Alex took something to kill himself that would not show in an autopsy because they let him know he failed them and it was time for him to go out to eternity.
All just my thoughts.