You can expand on Sif's personality with the help of this:

As the Goddess of War, Sif was very intelligent and talented. Straightforward, with a passion for studying war strategies, she craved for the recognition to be an equal of any male warrior. However, she was held back by Asgardian misogyny, and felt herself being an alienated freak due to her dark hair and her choice to be a female warrior. Because of this, she had envied Amora, the Goddess of Love, for a while, probably because of her conventional beauty. But, since Amora treats her like an equal, Sif didn't hold any sort of resentment for her, having to reluctantly give the same amount of respect, in return. While she possesses excellent maturity upon her being, Sif had a very close friendship with Thor and Balder, initially having a love dilemma between them, until Thor chose her to be his wife and queen; she still remains as a close friend to Balder, after this happens.

Also, add this to her family:
Hela (sister-in-law)