What do you call your brothers wifes sister?

Answer 1

i believe that your brother's wife's sister is also your sister in law

No, I think not! But as you seem to have the hots for your brother's wife's sister, you can call her "honey" if you like.

Answer 2

Your brother's wife is your sister-in-law. His sister is not called anything. She may be considered family to you though.