from his post, I can conclude that him and his fiance come from two different cultures. With that in mind, I'm sure he was and is aware of the intermixing of the two culture before the woman became his fiance. You don't become someone's fiance overnight. He's most likely thought about differences in religious beliefs, culture and how that will affect their children's upbringing.
It's okay and it's normal for a couple to have disagreements. Issue's like these come up all the time. And try and consider the situation from the girl's point of view as-well. She might feel like her family's needs are being a burden to her relationship hence her telling the OP that it's her family and she should deal with it. OP is dealing with the situation correctly.