The Gills boss and youth team coach Mark Patterson have also released six other second-year apprentices.
Patterson is also leaving Priestfield to oversee Ryman South side Ashford Town's new football academy.
Essam, 17, joined the club's centre of excellence in 2002 and has captained the youth team this season.
He has been a regular for the reserves for the last two years but is yet to make his first team debut.
Rance, 18, has been on the Gills books since the age of eight and is currently on-loan at Maidstone United while former Tottenham youngster Charlie Stimson, 18, also currently at Maidstone United, was on loan at Redbridge earlier this season.
The club will be releasing Conor Quinn, Ollie Bartrum, Liam Geering, Joshua Sargeant, Tom Murphy and Callum Day.
Source: BBC Sport
Source: BBC Sport