Fatae and Cousins

The Fatae contain both human-shaped magical beings and non-human-shaped ones, but in general "The Fatae" refers to the human shaped ones. The original Fatae no longer set foot on Albion's land (at least not without a lot of preparatory negotiation), but there are a number of human-descended lines of Fatae who still live in Albion.
The best known (but not only) ones of these are known as the Cousins, descended from seven sisters, sometimes known as the Grandmothers, or the Shining Ones.
The seven lines have particular magical inclinations and obligations, working on their own projects most of the time, but sometimes coming together for specific goals (and of course the occasional sizeable family gathering...). Each line maintains several large manor houses or equivalent spaces around Albion, and there are also spaces (as seen in Seven Sisters) in Trellech and London as well.
Old As The Hills shares a different experience of the Fatae, incluidng how they are seen outside of Albion.

Details about Old As The Hills

At one point, Rathna Edgarton meets one of the Fatae in an ancient pre-historic cave in the Pyrenees, in a discussion relating to portals in France. Back in Albion, Gabe makes an agreement with some of the Fatae for the good of the country.

The Grandmothers

The Seven Sisters use the names of the stars of the Pleiades, but it's entirely unclear (even to the Cousins) if they are actually the stars, if they are beings out of those ancient myths and legends, or if it's just a convenient set of names for them to hook onto.

• Maia is the eldest, resolver of enchantments.
• Electra turned her face away from Troy with sadness. She is most entangled with humans, focusing on philosophy, logic, and ethics.
• Taygete is the hunter, focused on transformation.
• Alcyone is the kingfisher who teaches astronomy.
• Celaeno is the mistress of hidden and secret things, often known as "the dark one".
• Sterope is interested in handcrafts, science, but also lightning.
• Merope is generally considered the youngest, wooed by Orion in myth. She cares particularly about voyages and protection of sailors. Merope's Speakers are under her protection, and there is a secret cult devoted to her at Dunwich.

Cousins

Seven Sisters and Fool's Gold focus on Cousins.
Cousins age more slowly than most humans - a Cousin in his early forties might look like mid or late twenties, one in her sixties might look like her forties. They tend to live longer, as well, seeing two centuries isn't terribly uncommon. Usually they spend their younger years (between visible adulthood in the larger world and their eighties or nineties) in the larger society of Albion and the rest of the world, before retiring to one of the family estates and focusing on the Cousin and Fatae magical obligations.
Because of this, very few Cousins attend any of the Five Schools (they're not ready for it when they're the right age, basically), and are instead privately tutored.
The way the Cousins work magic is different than those in Albion. Shared magical workings are often rooted in dance, particularly in a style that would be recognisable to many as Irish or Scottish step dance, up on the toes with very precise patterns both as an individual dancer and in larger groups.

Near-Cousins

There are some people who are not directly descended from the Seven Sisters, but who are affiliated with the larger community (usually known as Near-Cousins). They often have roles tending to places or beings who find having opposable thumbs or human-shaped mobility around handy. George, in Fool's Gold is one.