Sperm donor

Okay so we are pretty sure that my husband is why we can't have kids. His mother is convinced as well. He has a chromosome imbalance that can cause infertility or even late term miscarriages. His mom had it as well but still carried 5 children to term. I've read up on his imbalance and if we did have children by miracle we could end up having complications and baby could have issues. We have been discussing donors but he doesnt like to think he'll never have his own biological children. So this is where it gets a little weird for me. If we have a donor he wants to ask his only full biological brother however that seems off to me. I'm not sure if we should ask him or find a private donor.