I was struck by MG's description of them like "gasoline" and "fire," insinuating that the combination was more deadly than either alone.
But, I think the necessary deaths of spouses and of her children were a construct of Chad's. He was overheard making comments that the plan couldn't move forward as long as the spouses were alive. Lori (in the past) just divorced and moved on. I think Chad wanted them to seem (as a couple) as though they hadn't dumped their spouses (because that would sully his reputation) but rather that they were righteous widow/widower, which would be more attractive to their followers.
LV already had money and a much better-looking husband. The only thing Chad could offer was something she viewed as "spiritual superiority," and I think he played on that. LV is narcissistic (JMOO), and she craved being a goddess.
Chad came up with the perfect story to justify the killings. Lori is a murderer, but Chad is more dangerous and evil than anyone suspects. JMOO, of course. He is the fire and LV is the gasoline to my mind.