As i am not running edis i am not know with that. But you mean you have two injector grounds both firing two injectors and only one driver on the megasquirt?

I installed a second driver by changing the soldering of the ms. Then you can put em 1 on 1. But guess there will be an easier solution. Probably you can connect all 4 on one cable with the right settings in ms. But double check it as i am not sure.