...insomuch as nine clans at once can be summarized quickly :P

There's some discrepancy between the dates listed here vs the dates listed on a few clan leaders' separate submission, for the time being the dates here are to be considered the accurate ones.

Elsis: Loneliness/depression, ascended 26500 years ago, slain 9000 years ago by Fahgi
Clan quirk: Clan members have extremely dense bones that are almost impossible to break; the effect is wholly magical and invalidated by death. This quirk does not carry over if the child is born into a different clan.
Clan summary: Before her death, they were a gentle and loving clan, dedicated to easing the pain of others. Since then, due to millennia of cohabitation with Clans Melsir and Fahgi, they have become much more conniving and abusive. However, they remain the most peaceable of the three clans.
Clan strength: Excluding Shawnee and her followers, 18. Following mass conversion to other clans, declared formally extinct at DMFA+446, wholly extinct at DMFA+499

Fahgi: Betrayal, ascended 51200 years ago, slain 9000 years ago by Clan Elsis in retaliation for her death
Clan quirk: Clan members are born with hooves and dark base colors. This quirk may carry over if the child is born into a different clan.
Clan summary: An assassin and seducer, his clan consisted mostly of them same. After millennia of cohabitation with Clan Melsir, they have become far more aggressive on both fronts.
Clan strength: Excluding Shawnee's followers, 12. Following mass conversion to other clans, declared formally extinct at DMFA+446, wholly extinct at DMFA+473.

Melsir: Hate, ascended 36500 years ago, disappeared 2300 years ago
Clan quirk: Children of Melsir-clan Cubi are born small-sized regardless of their parents' size or what clan they are born into.
Clan summary: MURDER. Lots and lots of murder. Demonstrably a bad influence on Clans Fahgi and Elsis in the millennia since absorbing both clans. They have extreme reactions to Quoar-like Cubi, to the point of kidnapping infants from other clans to raise as their own, or murdering them. Adults they will attempt to either seduce or assassinate. However they seem indifferent to Quoar-like Cubi within their own clan, seeing "the problem" (whatever that is) as having resolved itself from the start.
Clan strength: Excluding Shawnee's followers, 87

Shawnee: Depression, 2009 years old, ascends at age 2396 - born into Clan Elsis
Clan quirk: If Shawnee changes her wing colors, the change applies to all members of her clan. This quirk does not carry over if the child is born into a different clan, but the natural chances of the child having the same color wings as their parent at the time of conception is unaffected.
Clan summary: A mix of Elsis, Fahgi, and Melsir Cubi, they are often aggressive if not outright violent, the Melsir ones especially. The quirks of all three clans mix randomly throughout the combined clan for the first few generations. Conversion into the clan is welcome, but seems to be the only time Shawnee interacts with the clan on a personal level, having apparently been traumatized by her own ascension.
Clan strength: 48 at ascension
(I've redesigned her clan symbol to be less exasperating X3 )

Sanst: Shame, ascended 57300 years ago, slain 1343 years ago
Clan quirk: Clan members do not experience loss of visual clarity based on light level (other visual impairments still apply). This quirk does not carry over if the child is born into a different clan. Cubi with Sanst parents or grandparents live significantly longer than Cubi of comparable heritage.
Clan summary: Clan is too scattered to effectively summarize as a whole.
Clan strength: Undefined. Nalia, the only survivor not to convert to another clan, has been vague about the number of children she's had since Sanst's fall and how many of them are actually in Clan Sanst, as well as seemingly not counting her grandchildren+ when making her calculations.

Ambrose: Curiosity, ascended 1343 years ago as Sanst's chosen heir
Clan quirk: Clan members are born with white fur / skin / wings; color fills in within three months . This quirk may carry over if the child is born into a different clan. In children with duality wings, the bat part starts as light grey.
Clan summary: Members of Clan Ambrose are generally quite intelligent, though they can be fairly hyperactive or sarcastic, with a taste for mischief. Most clan members have a specific point of interest that they focus on, and they tend to seek employment in education or research. If two clan members are focused on the same subject, they become fiercely competitive.
Clan strength: Currently undefined, 36 by DMFA+300

Ambrosia: Jealousy, 662 years old, ascends at age 1432 - currently a member of Clan Zezzuva
Clan quirk: Ambrosia-clan Cubi have matching hair and eye colors. Bald races will have markings on their heads. This quirk may carry over if the child is born into another clan.
Clan summary: A large clan whose only purpose seems to be to grow even larger. Despite having a female leader, female clan members are less valued because they can't breed as fast. Ambrosia herself is nasty, short-tempered, and hates to be questioned. There are conspiracies against her almost as soon as she ascends, likely before.
Clan strength: Undefined. Between her male descendants massively exploiting the Zezzuva twin quirk*, not tracking how many female descendants she even had, Ambrose "rescuing" female descendants or their own fathers shuffling them into the remainder of Clan Zezzuva instead of sacrificing them to Ambrosia, and centuries of her descendants converting to other clans rather than support her, the clan is a massive tangle of confusion by the time she ascends.
*I write under the assumption that all Cubi born into Clan Zezzuva are born twins regardless of who the mother is

Premi: Guilt/grief, 1596 years old, ascends at age 3117, birth clan unknown
Clan quirk: Cubi born into Clan Premi are inherently carnivorous, a trait of Premi's race. Unconfirmed rate of crossover as clan quirk versus pure genetics.
Clan summary: While not officially a pacifist clan, they trail in the wake of other clans to feed off the emotions of survivors. Travelers as a whole, but always in close contact with the rest of their families.
Clan strength: 24 at ascension

Ke: Surprise/confusion, ascended & disappeared 47300 years ago
Clan quirk: Ke-clan Cubi essentially "accumulate" the quirks of Cubi parents from different clans. For example, a Ke-clan Cubi with Quoar, Nact'Larn, Jin, Owona, and Kish'Ta heritage will be a Quoar-like female with pastel base colors, glowing eyes, and sharp teeth, and so will all her descendants, unless bred with a Cubi whose clan quirk conflicts with any of those, or by interbreeding within the clan which may "scramble" the results. If the child is not a Ke-clan Cubi, the quirks may all disappear within a generation or two, or even immediately.
Clan summary: Even among those still living who knew of Ke before his ascension, there is doubt as to whether he still lives himself. The few known members of his clan seem to be subject to some sort of brainwashing, referring to themselves as his daughters regardless of their gender identities and often going so far as to assault other Cubi - including Clan Leaders - who refuse to accept that Ke is superior to all.
Clan strength: Undefined / "the most".