Eh...It´s a little complicated...
First: Player one is always first character in list, player two is always second, player three is alway third and player four is alway fouth. Simple, ne?
Second: To use a controller in the second port you have to inplug it and chose on the second character in the character list (let´s say it´s Krator in second seat) I don´t really remember but you shuld go to the menu where you can chose what special attacks and magic you use. up on right side is a place where you can change from Auto to Semi-auto to manual. Cose Manual and done.
Note: multiplayer is only in battles...