Things we know about Grimm powers thanks to s02e01:

– It’s inherited
– Women become aware of their powers earlier than men
– You don’t know if you will have the powers until they hit you
– Even though it’s inherited, not every person in a family will have it

What we know about Nick’s Grimm familiy:

– His Great-Great Grandmother, Great Grandmother, Grandfather, Mother, and Aunt Marie had the powers, but his Uncle George did not 
– Nick’s Grandfather started to teach Kelly and Marie about Grimms and Wesen as soon as they exhibited signs of their powers