A married couple.
Husband call wife like Tarzan call Jane. :U
Of Course husband and wife can bathe together.
Unless you are in a polygamous marriage, you are your husband's wife, so you would call her your mother.
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."
Your Brother in law's wife
In Islam, it is permissible for a husband and wife to bathe together as long as they observe modesty and privacy.
The wife of a husband is referred to as the mother-in-law to her daughter's husband. In this relationship, the daughter's husband is the son-in-law to the wife. Thus, the connection can be summarized as the wife's relationship to her daughter's husband being that of a mother-in-law.
The sister of your husband is your sister-in-law.
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."
Trouble.
Domestic violence?