Indian Culture, Giving Children to Siblings

I am an American woman with an Indian boyfriend. We are very serious, respectable, and don't live together. We are discussing engagement and marriage.

In his family, if a brother cannot have a child, they ask their brother for one. His oldest brother only had sons, and his middle brother just had twin girls, and gave the oldest brother one of the girls because his older brother wanted a girl. I am appalled, and I don't know how someone could give away their own children, even to a sibling. How could his brothers or their wives do this? I am afraid that if he and I marry and have a son and if his middle brother wants a son and can't have one, he'll ask us for one and I'll be pressured into giving away one of my children.

Is giving away children to siblings normal in India? In America, giving away children is only practiced under dire circumstances, like if the parents are somehow unable to care for the child. His brother and sister and law that gave away their daughter were able to care for their child. Please explain to me if giving away children to relatives in India is normal. Please also explain the logic behind it. Maybe if I could understand it I wouldn't think it so awful. In America, it is a given that if you marry and have children that you will keep them all.

I love my boyfriend very much and we are talking of marriage. Do you think that maybe his relatives wouldn't want our child because it'd be half white American? I love this man very much, and don't want to run away from him if there is no danger. I also want children very much though and wouldn't want to give any up. It would be unthinkable in my culture.