You can set controll up in the Input Manager, and you can also choose the device index for the Action. So if you have for example two xBox Controllers, one of them has the index (The index is like the Number of the Controller) 0 and one has the index one.
You can then set up actions for the Controller 0 and set the same actions up for the Controller 1. Now you can use them in your code.
(Naming them accordingly really helps in this case, e.g 'snes1forward' and 'snes2forward')