Your husband's sister is your sister-in-law. Your husband's sister's husband is your husband's brother-in-law. But you are not related to your husband's sister's husband
If Jane and John are married, and Jane has a sister, Jane's sister is John's sister-in-law. Jane's sister's husband, however, is not related to John, although he is ''Jane's'' brother-in-law.
These people are part of your extended family. They are not related by blood to you and there is no simple word for the relationship. They are your husband's sister-in-law and brother-in-law, of...