Maybe.....

As for your other questions:

The Tahjai currently are an order of magic users (though not every magic user is automatically part of the Tahjai)
They have several divisions but I'll explain that a bit better with the lore expo.

Whilst they have great power and dominance, they do not rule the Empire, but manipulate quite a great deal behind the scenes.

The Teryn is basically another word for Lord/Nobleman & it is also a title for the leader of representative of a house/family.
So currently Scylla's master is the young Teryn Varros Avitus, since Eilis killed his father Teryn Balbus Avitus.
As for the girls, the 'covenstudents' they are essentially sold into slavery, their parents often are promised wonderful lives, whilst in fact most 'common magic users' go to these covens, depending on their skill or talents. They are observed at these places and there they determine what happens to the students. Whether they will serve a patron or family or whether they follow a more rigorous path with the Tahjai order itself becoming enforcers and such.
Most get sold into slavery though.
As for getting pregnant by the Teryn's well naturally it happens, but it is frowned upon by the right society, depending on the situation they decide what to do. Sometimes they kill the baby in the womb, other times they wait for it to be born and dispose of it then. But there are also more 'gentle-hearted' Teryn's that merely send the child away or sell it off into slavery as well. Technically they are his property so he can do with it what he likes.

One extra thing though: Scylla and Eilis did not go to the same coven. Scylla is also quite a bit older her path in life has been rather turbulent. 

Also if you should need me to play Alexa to have some more romance time for Toby you'll just need to let me know.