I think it is very unlikely you will be able to build a strong relationship between your child and his parents under these circumstances.

Any communication you attempt with his parents should be via your ex, and it sounds like he doesn't want to be involved with the child. Maybe try again with him after the baby is born.

Assuming the relationship with his parents doesn't happen, you can still educate yourself and your child about the culture and look for other places where your child could experience that part of their background, such as movies, books, music lessons, language lessons etc.

You might find a warm welcome at a Hindu temple, if there is one in your area.