I'm a lesbian who was dealing with just the IUI issue years ago. My therapist was adamant that using my brother-in-law's sperm would cause way too much family complication to be worth it.
I am currently doing DE/DS. The funny thing is, both donors seem to have aspects of me that I was looking for. Yes, I would rather it be OE IVF, but I'm too old for that.
I'm "no tell" so I'm not going to worry about having to explain details of conception. Once your brother or brother-in-law is in, he will always have a legal way to attempt custody of the child. We like to think that would never happen, but the truth is,no one knows what the future brings.
So I would urge you to keep youself and this child out of any possible complications....DE/DS is my advice...