You can be. If your sibling or cousin marries your wife's brother's wife then yes you are related. But there's no other way you could be related to them besides that way.
Your wife's brother's wife is not related to you. Your wife's brother is your brother-in-law. His wife is your wife's sister-in-law. So you would refer to her as your brother-in-law's wife or as your...
WOW! You are really on A quest.
This is my suggestion: Please yourself, Then if others are pleased then that is good collateral damage.
Ricky Nelson before the plain crash: You can't please...
The possessive of the singular wife is "wife's": your wife's car. If you had more than one wife (rather unlikely) you would have "wives" and if they had more than one car it would be "your wives'...