After joining the Mariners from Heidelberg United FC, Heffernan made seven A-League appearances for the Mariners.
Uskok signed with the Mariners in November 2015 and made six A-League appearances.
Stella arrived on the Central Coast as a January transfer window recruit and made eight Hyundai A-League appearances for the Mariners.
Mariners are looking to rebuild their squad after a disappointing campaign saw them finish the season at the bottom of the table.
