Hanging a door means scribing and cutting it to fit the jamb, but when the task is to install a pre-hung unit, the door can't be adjusted. The jamb must be adjusted to accommodate the door.
Gary Katz demonstrates how to make the critical adjustments in the hinge jamb, especially near the hinge locations. If you begin the installation by plumbing the hinge jamb, he warns, then nailing the jamb near the hinges, you will never be able to make those critical adjustments. That's especially true when you're installing a pair of doors.
Follow these steps so both doors are flush at the top and flush along the meeting stiles, with all hinge gaps of a uniform width.