[quote=@Styrgwyr]
These families, the Isamu and Rikimaru are more like Yakuza groups right? You don't have to be a blood-related relative to be part of the "family", right? 
[/quote]

Yeah, you've got the right of it. There are Mages in each group who are blood relatives of the Rikimaru or Isamu, but generally any Mage willing to affiliate with a side is welcome.