You would befriend a befriend soon to be husband's sister the same way you would befriend anyone you wanted to be a friend of. Try planning events involving the three of you, that way you can get to know her better and it wouldn't be as odd. Also, try finding things she likes that you could do together.
sister in law
Your brother would call your husbands sister by her first name. Or, "my (sibling's) sister in law.
Your Sister-in-law
you call her your daughter's husband's sister
Mom
brother in law
No. Your husband's sister-in-law is either your sister or the wife of one of his siblings. If she is the wife of one of his siblings, she is not related to you.
Because the sister isn't the same person as the ex, and they remained good friends, for instance.
Sister-in-Law
jacquline
Yes, I suppose that they would be sister-in-laws. Because your sister is your husband's sister-in-law, and the other sister is his sibling, then I suppose they would be sister-in-laws.
You befriend Mirabelle and soon after she will bring you a dog. :-) good luck!