If your daughter and husband are fighting constantly sit them down( separately) and ask them something like "what is the matter with you guys?!?!?" then when they answer say "well okay so you have problems with each other " "that doesn't mean you can fight!"
Your daughter's husband is your son-in-law.
daughter
You daughter's husband's mother is your daughter's mother-in-law. The English language has no term for a relationship between you and your daughter's mother-in-law.
The daughter of your husband's brother is his (and your) niece. Her daughter is his (and your) great niece.
no you have to say: my husband, my daughter and i ....
The daughter of your husband's brother is his (and your) niece. Her daughter is his (and your) great niece.
Your daughter's husband is your son-in-law.
There is no connection. They share no common ancestors. In introductions, he would be referred to has her cousin's husband.
Your husband's niece is your niece, too. You and your husband are her aunt and uncle. Your brother is not related to a niece of yours who is the daughter of your husband's sibling.
The daughter of your husband's brother is your niece.
Your mothers husband would be your step father and you would be a step son or step daughter.
Your husband's cousin is not related to you. His/her daughter is not related to you either.