The wife of your brother (younger or older than you) is your sister-in-law.
younger brother's wife -- maradalu elder brother's wife ---vadina
Brother in-law
You would refer to your younger brother's wife as "bhabhi" in Hindi.
The wife of your brother is your "sister-in-law" In English, this is true whether the brother is older or younger than you are.
Your younger brother's wife's sister's daughter would be your son's cousin.
No, as it is a flirting move so your brother might suspect there is a connection between you two!
Baldo is the younger brother of Leon.
In English, the wife of your brother (elder or younger) is your sister-in-law. If you have a child, she is your child's aunt.
Your younger brother's wife is your sister-in-law. Your older brother's wife is also your sister-in-law. In English, we make no distinction between the two. However, when talking to your sister-in-law you do not address her as sister-in-law. You just call her by her name.
If it is your brother's child, she would be your "niece." If the daughter is not fathered by your brother, then she is your "sister in law's daughter"
In the English language there is no difference between the wife of an elder brother and the wife of a younger brother or of a twin brother. The wife of any brother is your sister-in-law. If you are actually talking to her, however you should just call her by her name. Nicknames are fine too.