Brockel was slated to become a restricted free agent, and Williams an unrestricted free agent.
In his three seasons with the Panthers, Brockel has four catches for 25 yards and four carries for 13 yards. He finished third on the team with six special-teams tackles in 2013.
Williams started last season as the Panthers' starting right guard but suffered a season-ending knee injury against the Seattle Seahawks, the team's season opener. Williams has played in 40 games (21 starts) over four seasons with the Panthers.
The Panthers also tendered contracts to offensive linemen Byron Bell and Chris Scott on Monday.
Bell has made 40 starts at right tackle during his three-year career while playing in all but one game since joining the Panthers as an undrafted free agent from New Mexico in 2011.
Scott, 26, played in 10 games with eight starts in his first year with the Panthers.