"My grandfather's name is not Aamir but Raj."
Translation:मेरे नाना का नाम आमिर नहीं राज है।
1. दादा (dada) For father's father
2. नाना (nana) For mother's father
3. दादाजी (dadaji) the ji is added to many words to show respect. And it is more usual to hear dadaji than just dada.
4. नानाजी (nanaji)
Don't forget that with a noun, "X नहीं है" means "is not X" and therefore you can derive that "X नहीं" on its own means "not X." Don't forget that this is a language that uses postpositions, not prepositions. (You use the equivalent of "prepositions" to modify things from behind.)
(X में = in X, X से = from X, X पर = on X, etc.)
So "आमिर नहीं राज" means "Not Amir, Raj."