Here in Philippines we are calling aunte and uncle for all people who we think is already married even if they are  not part of the family or we don't know them ( like its our first time to meet them or just some people in the street ). We also calling people Kuya (older brother) ate (older sister) for all people who are older than us but not married.

For family - I just call aunte and uncle those are married relative which are not my cousin.  We call grandma and grandpa for those who are very old already. Whenever I will join family reunion it's very hard for me to determine how am I related to them since Filipino family are very close to each other that even 3rd degree cousins still know each other.. Even the cousin of the cousin of your cousin which might be not your cousin anymore you will think that she/he is your cousin.

If I get to know that that woman is my friend's aunt, I wouldn't care if she's his father's sister or his mother's sister. That doesn't matter I think.

I DO agree with Susan612. You can simply say "maternal" or "paternal".

With grandparents you also say maternal and paternal grandmother or grandfather, but you wouldn't call them that as a name. There are a variety of names that people use for grandparents:Nana, Granny, Grandpa, Pop. In my family, we called my maternal grandmother Nana, and my paternal grandmother Grandma. My maternal grandfather was Pop-pop. Sometimes we referred to both of my grandmothers as Grandma, but added a last name to distinguish them. My neighbors called their paternal grandparents Nanny and Poppy and their maternal grandfather was Zayde, a Yiddish word for grandfather. I don't remember what they called their maternal grandmother.

"I also have the same question, for example, my father's mother and my mother's mother stay together, when I call "grandmother", who will answer me?"

No one, because they'd be insulted you don't know their names!