Ultimately this is all academic, because there's no real way to make "Bruce is actually Terry's dad/granddad" work, because that change betrays something fundamental about what makes Beyond such a good show. One of the show's strongest ideas is that Batman is made, not born. Terry, in the original series, has no genetic connection to Bruce. He's just a street-smart kid who gets into trouble and is handy in a fight. But when his father is murdered he develops a thematic, a spiritual, connection to Bruce. Terry has lost a parent just like Bruce lost his parents, and both of them lost those parents to the criminal element of Gotham City. Terry even bothers to bring this up in the pilot movie. What unites Bruce and Terry isn't genetics, it's shared tragedy, and the willpower that both men have to use that tragedy for good.

Making them related betrays this idea. It was a terrible decision.