Killing the ex husband makes no logical sense. He is as probably paying significant sums in both spousal support and child support. The only ‘logical’ motive would be to have full custody of the kids and then be free to move. That seems like a somewhat trivial excuse to kill someone who is paying you lots of money. Obviously this is 100% speculative and who knows what other internal disputes they had going on, just thinking out loud.
Possibly however a couple of the victims family members were on tv recently commenting on how even after their divorce the ex-wife was constantly being unbelievably difficult when it came to shared custody of their children.
Something to consider anyway.