First add the background, players, and solid instances into families. You will need two families; one for sprites, and one for tiled backgrounds. You will need to add two global numbers: Dy and Dx. Both are set at zero. Now, add a group and call it "split-screen". In that group, create a blank condition. For the actions:
To finish this off, add another group called "Game" and put in it the players' controls. When the left and right / 'A' and 'D' are down, don't forget to set the players mirrored / not mirrored.