I agree, a simple custody dispute would focus just on the mother. There'd have to be some sense of betrayal or a long standing hatred of the mother's family, exacerbated by the custody dispute.
A custody dispute would focus on the mother. But would it not focus on the Mother’s immediate family as well? Let’s talk hypothetical for a moment.
Say said father of child has said mother of child killed.
The father stands a risk of being caught. When he’s caught he goes to prison.
Who’s going to get the child who’s mother is now deceased and father is in prison? Would it be the murdered mother’s family or would it be the convicted father’s family? The courts would undeniably place the child with the family of the the mother.
Now, if you consider the two families, perhaps they had more in common than a minor child. They could be long time friends, they could have partaken in some business ventures together, they could have even been each others confidants.
What happens in a child custody dispute? Both sides want to win and will most likely air all the dirty laundry they can against the opposing side.
I believe a custody dispute very well could have been the “straw that broke the camels back”
The W’s could have initially used things such as housing and living situations as one of the reasons to gain custody. It appear Chris fixed that problem a month before the murders.
Also, there'd need to be a father's family where both grandparents were intensely invested in gaining sole custody of their grandchild, and who had other social/psychological issues that made them into psychopaths around gaining custody: feeling entitled, convinced they were smart enough to get away with it, wanting to take a nuclear option to settle the matter.
The W’s already have one grandchild in their care along with their other son. I’d suggest researching how they gained custody of that child.
For eg, in the ongoing case of Dan Markel, allegedly murdered on the orders of his ex-wife's family, the dynamics of the accused are a wealthy family dental practice, a grandmother who's life is apparently totally invested in her children and grandchildren, and her son who despised his ex brother-in-law and who's favorite TV show is probably The Sopranos..
The four W’s in question may not have what we all see as outward wealth, but they do have a lot of money standing behind them in the one surviving and one deceased elder W.
All JMO, but the W’s has the motive, means, and skills to pull this off. They check off every box on the list-knowing where all the family lived, knowing the homes, knowing routines, wanting control over a child, money to back them up, hunting skills and patience needed to pull this off, exacerbated by a recent birth of a child that wasn’t JW’s ensuring that HMR & JW likely would never get back together. And just in case it was his, there was no risk taken to kill an unborn child but the murders were committed just after the child was born. JMHO.