Borderlands: Scooter’s Parentage…

As I was approaching Mad Moxxi’s joint in Borderlands‘ third DLC, Scooter comes on the intercom, admonishing me (the player-character) to be nice to Moxxi… “on account of her being my mom ‘n all”.

So, if Moxxi is Scooter’s mother, then what is his relationship with Marcus, the gun-runner? And who is the little girl in the opening of the first DLC? :-?