An Aunt.
sister friend
Aunty and Uncle.
Aunt
You would call your father's sister "பெரிய அந்தை" (periya anthai) in Tamil.
philapple Uncle
Sister in law
Your mother's sister is your aunt.
The relationship of the sibling of your sister-in-law or brother-in-law to you does not have a name in English. You could call them your brother- or sister-in-law if you want, or you can call them the brother or sister of your brother- or sister-in-law.
Brother-in-law
cousin
The English language has not special term for the husband of your sister-in-law. You woudl call him your "sister-in-law's husband."
sister in law