We're also from Pittsburgh and we try to avoid PHL too.
When we can't book through CLT, we make sure we take an early afternoon flight back arriving in PHL early enough to have at least 2 flights to PIT left. So far, it worked out well.
We also return on Saturday and the flights from PHL to PIT have never been full that day.
Hope you won't have any problem this year. Enjoy the trip!