Being a former family law attorney (in Texas, though, not California), the mandate of the family courts is to do what is in the best interest of the child, not the parents. If it has been shown that Zach has been responsible for Cody his entire life, and that Shaun and Zach have had the sole caretaking responsibility for him over a long period of time, then the odds of them getting custody of Cody are extremely good.

In Texas, when a child is at least twelve, they can file an affidavit of choice of conservator. The court doesn't have to follow the child's wishes (still a child, after all), but it is something the courts can consider.

Children do best in stable homes with support and continuity. The courts do the best they can to ensure it.