The Fifty Families are the current ruling houses of Europa. Many of them are Sparky lineages, but some of them are just old-fashioned royalty. Many Spark lineages are considered separate from royalty like the House Mongfish. They do not much like Klaus's rule over them, but can't do anything about it, at least openly.
The Other War saw the total destruction of forty-three major houses - whether this included the Fifty Families of the era is unclear.[1]
The Storm King conspiracy references the Fifty Families, claiming that their Storm King is one that the Families will officially recognize (mostly because he will restore their power). Whether this means that the Families are actively involved in the conspiracy or simply a predictable element is unclear.
Agatha H. and the Clockwork Princess reveals in a poem that every one of the families wants to have one of their own recognized as Storm King.
The fifty families play a game
That all revolves around a name.
To play the game you must be skilled
The Game of Kings can get you killed.
They plot and murder, lie and sin
Determined no one else should win.
They'll turn Europa upside down
To try to claim the Lightning Crown.
- Anonymous (No, really, we don't know who wrote it. Honest.)[2]
Resurrection[]
The Fifty Families have strict rules and social taboos against resurrection. Revived individuals are apparently removed from lines of succession.[3] As Gil explains to Moloch ✣ , "…someone who's been waiting twenty or thirty years to assume power- doesn't much like it when their predecessor goes and gets reanimated." Resurrection seems to be reserved for those sneaky enough to hide that it occurred, or powerful enough to ignore the social consequences.