OK, I'm married to my husband which makes my brother and him brother-in-laws. If my brother gets married, my brothers wife becomes my husbands sister-in-law, right? And if that's true, why isn't my brother and my husbands brother, brother inlaws. It seems like they would be closer related because they're me an my husbands direct family.

The reason is because you and your husband are the link when it comes to in-laws. The marriage between the two of you creates the in-law link to each of you alone. All of your siblings are his in-laws, as yours are his. Extended family doesn't enter into the equation as far as terminology, and that is where I think your confusion is. Siblings to each of you are not direct family when you are married, but are considered extended family to your marriage. Your brother and his brother are simply each of your siblings. They are not married into each of your families, therefore they are not considered in-laws to each other or related to each other. If it is hard to understand consider both your husband's and your's sets of parents. His mother & father are your in-laws, as yours are his. But, they aren't considered anything in relation to each other as couples. So, your folks each refer to the other when talking with their friends, "my daughter-in-laws (or son-in-laws) parents." It is the same with the rest of your extended families. Your brother would refer to your husband's brother as "my brother-in-law's brother." Obviously, it doesn't mean that they can't be friends or refer to each other as "family." It is just extended family. Society hasn't created any special wording or terms to call them anything more than that.

She would be your sister in law, but not your husband's.

Actually HG, she would be her husband's sister-in-law too. But it is called sister-in-law by marriage, not blood related.