Here is my first thoughts on the grid.
Players place their 3 pieces in either corner on their side of the board. Filling the corner square and the one below or above then the square to the right or left. Depending on the side you start on.
Players will use 1 dice and grid movement. Moving Up,Down,Left,Right starting for the piece’s position. As a piece is moved it fills in the squares it lands on with your color. Before you roll and if you are next to an opponents filled square you can un-fill their squares instead of moving. If your piece is surrounded only by your opponents color it can no longer move. You also can’t move onto filled squares of your opponents color.
Occupying the same space:
Is to fill as many squares as you can before all of your pieces are trapped.
For the game your making for the course you should call it “Off the Grid” hahaha