I think someone like CD could be easily swept up in the charm, sexuality, and hero worship/admiration of LV. It happens pretty routinely to men in their 50s, to fall for a sexpot and discard their hard working wives of decades. I know personally men who have done this (without killing anyone).
I'm afraid the problem might have been JJ, he was very high maintenance.
As long as JJ was around, LV and CD couldn't be romantic newlyweds, or go off together to live in Hawaii. If they truly believed Doomsday would be in July, they didn't have much time to be together.
There have been cases of women who have killed or abandoned their small children in order to go off with a man, who they know isn't interested in their children. Like Susan Smith, but others I know of.
Possibly TR was eliminated because she cared so much for JJ and would know if something happened to him. Also, TR may have come into conflict her mother (and uncle), because of the many bizarre things happpening/deaths in the family. And she may have inherited money from her father, that LV wanted to use.
IMO, LV planned with her brother to eliminate her husband, CV, and get the million dollars. Then she could get someone else to look after JJ, possibly his grandmother.
But LV did not receive the life insurance, the grandmother did. LW, the grandmother, has said it herself: out of pure spite, LV didn't want to send JJ to LW, because then LW would have everything, and LV would have nothing, she would lose the financial support for JJ.
Again, possible with the obsession about Doomsday, LV thought this was all short-term anyway, that whether people were alive or dead now, or whether she might be arrested and go to jail, didn't matter because the end of the world was coming.