That all of them helped in the plan to keep Tabby away from her son, giving George complete control of him, is one more motive for George to go along with helping Jake keep HR away from her daughter - giving Jake complete control of her.
As Betty pointed out, another reason for George to support HR's murder was her support of Tabby wanting more access to her son. Hanna could be supportive of Tabby getting custody etc....Hanna could "gang up"
with Tabby, "compare notes" etc....Facebook hacking showed they communicated.
Also, George bought into the lies about Elizabeth, that she could not be trusted around the children, thus, he didn't trust his niece being around any men in Hanna's life. George was paranoid about SA. George said to protect S, he would take her away from Jake and Elizabeth.
Point is, we have been saying for years that George had "no skin in the game" no reason to involve himself in Jake's custody issues. But George did have some of his own personal reasons for wanting Jake to get what he had, full custody.
George and his family were right in the middle of a plot to keep Tabby away from her son long enough for George to claim she had abandoned him.
All my opinion.
And I think George liked the idea of raising the 2 children together. It was a benefit to George for his son to have a child his own age to play with, to be home schooled with, etc....
The Wagners committed crimes together, did everything together, even ran errands together and this includes planning murder together.