Mahelona, a former draft pick of the Tennessee Titans, joined Bryant on the inactive list Sunday against the Patriots, while Robinson was in uniform and saw action.
The move left the Dolphins with 52 players on the active roster, but that number will drop to 50 once Brown and Hill are placed on injured reserve.
That means that as many as three new players will be added to the roster.
According to The Miami Herald, defensive end Quentin Moses and safety Lance Schulters already have been signed, but that wasn't official as of Wednesday morning.
It would be a return to Miami for Schulters, who played for the Dolphins in 2005 before spending some time in Atlanta last season.