Re: how do u introduce....
I introduce them by the true relation. i.e. brother-in-law, sister-in-law etc.
My wife calls my parents ammi abbu but she introduces them by their true relation as well. i.e. MIL, FIL, SIL etc.
It doesn't matter what you call them at home (i.e. aunty or ammi) but one should always tell others at least once how that person is really related to you. After that if you refer to them as ammi, the other person would know that by ammi, you are referring to your MIL.