not-technically-historically accurate system
...yeah.
Ok, guys...I went back to the rulebook to try to figure this out, and I think I have an answer.
Not only did they
Not Do The Research, they
Just Didn't Care that they didn't do the research.
Apparently, according to L5R canon, which appears to be strangely
bowdlerised mix and match of mostly Greek and Norse mythology and some other stuff with the names (mostly) changed out to sound more Japanese, a "clan" is an alliance of human families under the banner of
Hestia, Demeter, Hera, Hades, Poseidon and
Thor various children of the
titans gods. The Emperor is
Zeus Hantei, and they're all the sons and daughters of
Rhea and Cronus Lady Sun and Lord Moon. And they needed one more to get eight so the 8th clan is ruled by
Loki the evil brother. Oh, also since they apparently wanted an
obvious stand-in for the christian devil bad guy, they put in
the Nothing from Neverending Story the Nothing from L5R.
It all starts with the first several children of
Cronus Lord Moon and
Rhea Lady Sun being eaten by
Cronus Lord Moon. So
Rhea Lady Sun tricks her husband into eating a stone instead of
Zeus Hantei, who is raised by
the goat Amalthea various animals, grows up and fights with
Cronus Lord Moon to retrieve his brothers and sisters from his belly. During the battle he cuts
Cronus Lord Moon apart, and
his blood and semen only his blood falls to the earth to create
Aphrodite, giants and some other stuff humans.
At this point they decided that humans needed to be ruled, so they
met up with Goku at the World Tournament left Tengoku together and fought in a tournament to see
who was the strongest who would get to rule the world.
Zeus Hantei won the tournament, so they decided that he now ruled
the entire world an arbitrary corner of one continent that from looking at the map is obviously not the entire world. So he divided it up into different
tax zones areas and told
Hera, Hades, Poseidon and the other gods his brothers and sisters that they could rule these
tax zones areas and to pay him
taxes a tithe on the labor of the humans who lived there, whether they liked it or not.
And that's how
Equestria Rokugan was made.
That's the abbreviated version. There are also some guest appearances by the Norns, Odin and the Yggdrasil tree, a genderswapped version of the Hindu Lord Shiva (complete with four arms, but with three faces instead of five), a pre-human Naga empire that reminds me an awful lot of the one from World of Warcraft, a bastardized Bushido code that honestly reminds me of the eight virtues from Ultima except with humility removed, and some other stuff that's all blatant rip-offs of all sorts of things.
But short answer, according to canon, "families" are clans/families/great houses, and "clans" are the political units created by the gods dividing up the world amongst themselves, with any humans living in their designated zones considered their vassals.
I vote we forget about all that and go with what we have.