A: To do so can be rather complex and he really needs to consult privately with an attorney familiar with dependency cases. The rhetorical question that occurs to me is why he didn't take action when the dependency case was first filed.
A: No way to know. They handle paperwork as it comes in. Judges have to sign decrees and who knows how high the pile on the desk of the judge who got the proposed decree may be. Plus it's the holidays and so court filings are usually much higher in number while the court house personnel are out for the holidays and to use their "use or lose days."
If you e-filed the paperwork you may be able to see when the decree was signed online. Otherwise you'll have to wait for communication from the court in the form of a final decree.
A: In PA 50% -60% of your disposal income can be taken for child support, depending on whether there's one or two families. So, as you can see, your second family was essentially take into account in your order.