The deals were completed Thursday, five days before Harbor and Young would have become free agents. Bradfield was a restricted free agent and has the most experience of the three. He started 11 games at left tackle last season, filling in for injured rookie Luke Joeckel, and started 12 games at right tackle in 2012.
General manager Dave Caldwell says all three "have experience in our system and will compete on a daily basis."
Harbor was claimed off waivers from Philadelphia in September and finished with 24 receptions for 292 yards and two scores.
Young was claimed off waivers from Buffalo in October and saw action in 11 games as a reserve.