I would add the PH for just you and nephew once you need them. Maybe you'll decide you don't want them and that's money you save.
Also, you could save by thinking about how many days your Dad is going to the parks. If he's not going to use all 5 days of his tickets, just buy the number of days you need for him. If he's only going for 2 days, buy a package with just 2 days for everyone. You can upgrade everyone else's tickets for the number of days they need. This only takes a few minutes and can be done when you check in. If he only wants 2 days instead of 5 days, that saves about $130...which could pay for the PH upgrade for you and your nephew.