Header for new window
I wouldn't mess with your kings. The biggest weakness in a wall of windows like this is stiffness. You want as much lumber going full-height as possible. 

Also, that's not a header. It doesn't carry any load and merely offers window flange mounting and horizontal stiffness. 

Pull the jacks, double the "header" (mullion, really) and toenail it in well, and carry on.