Ellis played for the Nittany Lions from 2019-23.
Hardy was drafted No. 219 overall in the 2024 NFL Draft.
Clifford was Penn State's leader in wins as a starting quarterback, passing yards, total yards, and passing touchdowns.
Castro-Fields appeared in eight games for the Commanders last season.
For the second straight season, there's a battle for Penn State's starting placekicker spot.
Prior to the 2024 season, James Franklin announced Cooper Cousins and Dejuan Lane will burn their redshirt this season.