she would be called your cousin. Maternal uncle's daughter is your cousin.
Cousin...
Your mothers brother is you maternal uncle.
In English, you call your maternal uncle's wife "aunt." It's not rocket science, honey. Just like how you call your paternal uncle's wife "aunt," keep it simple and call her the same thing.
In India we call them "Mama Ji" and in English we may say Maternal Uncle.
Yes, because that is what he is. He is your uncle on you rmother's side, so, your maternal uncle.
You could probably contact him on the phone, or via skype if you are tech savvy. If you mean the name of the relation between yourself and your maternal uncle's son, that would be a cousin (first cousin to be exact).
your great uncle
In Bengali, "dadu" means grandfather on the maternal side. It is a term of endearment and respect used to refer to one's maternal grandfather.
your uncle is your sons great uncle
Your mother's uncle, whether maternal or paternal, is your great uncle. You are his great nephew if you are male, and his great niece if you are female.
"Uncle" in Bengali is মামা (mama) for mother's brother or ফুফা (phupha) for father's brother.