(uncommon) One's brother-in-law or sister-in-law's brother; that is, one's sibling's spouse's brother (one's sister's husband's brother or one's brother's wife's brother). (in the plural) Men whose brother and sister are married to each other. Besides, is my brother in law's brother related to me?
Nothing. That sibling is legally and genealogically a stranger to you. Your spouse's siblings (full, half or step) and your siblings' spouses are all your brothers-in-law and sisters-in-law. So the brother of your brother-in-law (i.e. sister's husband) is simply your brother-in-law's brother.
Beside above, what is your husband's brother in law to you? To clarify: if the husband's brother-in-law is your own brother, then you call him whatever you've always called him (and refer to him as your brother). If he's your husband's sibling's husband, then you don't refer to him as your brother. There's no preciser word than 'husband's brother-in-law' for that in English.
Likewise, what is my brother in law's sister called?
Sylvia's sister is not technically related to you at all. You should call her Claudine, because that is her name. You can also correctly refer to her as “My brother-in-law Bill's SIL Claudine.”
Can 2 sisters marry 2 brothers?
Double Cousins A double cousinship occurs only when a set of siblings marries another set of siblings and both have children. This could be two sisters marrying two brothers. In your case, this is a brother and sister marrying a sister and brother. Double cousins actually share the same gene pool as siblings.
Related Question Answers
What do you call your brother in laws brother?
Nothing. That sibling is legally and genealogically a stranger to you. Your spouse's siblings (full, half or step) and your siblings' spouses are all your brothers-in-law and sisters-in-law. So the brother of your brother-in-law (i.e. sister's husband) is simply your brother-in-law's brother. Who is considered a brother in law?
The definition of brother in law is a man who is related to you through marriage to your spouse or sibling, not through blood. An example of a brother in law is your sister's husband. An example of a brother in law is your husband's brother. Can you marry your sisters husbands sister?
You certainly can. I am assuming that your sister's sister-in-law is not your brother's wife, which, while such a union would be legal and genetically sound once their divorce was final, would not be a very nice thing to do. However, marriage to your sister's husband's or wife's sister, would be wonderful! Can you marry your brothers wifes brother?
Yes you can that would be totally fine. But keep one thing in mind that both relations are different your sister in law and your husband. So if any problem occurs during marriage these relations should not get be mixed and get effected. What do I call my brother's wife?
sister-in-law
What do you call sisters husband?
sister-in-law The husband of your sister is your brother-in-law. Is it weird if two sisters date two brothers?
Double Cousins A double cousinship occurs only when a set of siblings marries another set of siblings and both have children. This could be two sisters marrying two brothers. In your case, this is a brother and sister marrying a sister and brother. Double cousins actually share the same gene pool as siblings. Can I date my brother in law's sister?
Dating Your Sister's Boyfriend's Brother. It's weird. He could potentially be your brother-in-law before he's your husband. If your sister begins dating a member of the same family you are, do everything in your power to end it, and avoid the struggles. What is it called when siblings marry?
Incest
Is a sister in law a sibling?
Sibling-in-law includes the brother-in-law and the sister-in-law. It refers to the sibling of one's spouse, or the spouse of one's sibling, or less frequently the spouse of one's spouse's sibling. What do you call the son of your husband's first marriage?
I'd be super happy to be called “dad”, and to call him my son, but I would completely understand if he wasn't OK with that, or if his biological father wasn't. If he wasn't happy with “dad” and “son”, or “step-dad” and “step-son” (eww) I'd be happy with first names. 
