How wonderful that you want to show respect to your brother's wife! You can simply call her by her name or use a term of endearment like "sister-in-law." Remember, what matters most is the warmth and kindness in your heart when you speak to her. Just be yourself and let your love shine through.
probably by her name
Sister In law
A hoe.
aunt
We call "Mami" to moms brother's wife.
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.
sister in law
Brother-in-law
Pick up the phone
errrr, no maybe nephew
Shwe would be your sister-in-law.
Your sister-in-law.