Petersen spent nearly 20 years at Penn State.
Sowell follows his older brother Chase in transferring to Penn State.
The freshman did not get any playing time this season.
Brookins was with the Cyclones for one season, but preserved his redshirt and did not see any game action.
Manske is the sixth former Iowa State player to transfer to Penn State, following fellow quarterback Rocco Becht.
The former Iowa State player has four years of eligibility remaining.