Inter caste marriage in Mumbai

So, my sister is dating a boy from Airoli in Navi Mumbai, and they want to get married. Both are doing PhD from an IIT but have a 6 year age gap.( my sis is 27 the boy is 33)) And my parents are still on the way to be convinced because they are not so open to inter caste marriage. (We are UR category from Bihar and the boy is from OBC). So, I am also worried somewhat. Please let me know how accepting are the Maharastrians to other state people (specially Bihar, given its repute) and do a lot of migrants from other states live there? Will the language barrier be a big problem? Can an outsider adjust well?