Yes, you are only related by marriage. There have been marriages of sisters who marry brothers.
The husband's brother is a brother-in-law to the wife. The wife's brother is a brother-in-law to the husband. However, the husband's brother is not related to the wife's brother.
Your brother and your brother-in-law are not related. They can, of course, be friends. Your brother in law is married to your sister therefore he is your brothers brother in law also.
There are two ways to have a brother-in-law. If you have a sister and she gets married, her husband is your brother-in-law. Also, if you get married and your wife has one or more brothers, they are your brothers-in-law.
The plural form is brothers-in-law.The plural possessive is brothers-in-law's.Example: Both of my brothers-in-law's careers are going very well.
The singular form of the plural noun brothers-in-law is brother-in-law.
They are brothers in law
The plural form of the compound noun brother-in-law is brothers-in-law.The plural possessive form is brothers-in-law's.example: Both of my brothers-in-laws birthdays are on the same day.
Brother-in-law
Your husband's big brother is your brother-in-law. If your husband has a little brother, he is also your brother-in-law.
The compound noun brother-in-law is the singularform.The plural form is brothers-in-law.
You are your brother's wife's brother-in-law, if you are male. But your brother's wife can also have brothers-in-law who are not related to you or to your brother. They would be the husband's of the wife's sisters.
Your wife's brother-in-law is either your brother or the husband of her sister. In the first case, her brother-in-law's brother is you or one of your other brothers. In the second case, her brother-in-law's brother is not related to you.