I understand, this is not an online game?
If not, then:
1. create a sprite, an "eye", not Visible.
2. add a behaviour "SCROLL TO" to the "eye" (not to the character).
3. EVERY TICK: position the "eye, like this:
X = player1.X + player2.X / 2
Y = player1.Y + player2.Y / 2
It will always center the camera between both players evenly.