SOLVED. YA, 2 book series, main character called Verity, she loved to sail, in the first book, her grandmother was the antagonist. [s]

[Maryanne]

Verity's grandfather was i think a smuggler, and a leader of something called the gentry, but she only found that out in the first book. Her mother was pregnant, and her grandmother was there because (i think) she needed 3 generations of them for some kind of spell

[[deleted user]]

Mistress of the Storm?

[Kris]

Mistress of the Storm by M.L. Welsh - Kayleigh's suggestion

[Maryanne]

Yes! that's it.