Of Course husband and wife can bathe together.
Husband call wife like Tarzan call Jane. :U
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
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."
Nephew.
Your husband or wife, if you have one.
Trouble.
Domestic violence?