I think it is appropriate to call him your brother.
There is no specific word for the husband of your wife's sister. If you need a phrase, call him your "sister-in-law's husband."
sisters in law
Husband call wife like Tarzan call Jane. :U
She is your sister-in-law.
Unless you are in a polygamous marriage, you are your husband's wife, so you would call her your mother.
Brother-in-law.
Your sister-in-law.
your brother-in-law :)
A husband's stepfather is a step-father-in-law to your wife, but, if your wife is comfortable she can still call him dad and if not, she can call him by his first name.
There is no specific word for the husband of your wife's sister. If you need a phrase, call him your "sister-in-law's husband."
Phillipp uncle
Your Brother in law's wife