My brother wants to use my Hubbys sperm?

Because him & his wife have been trying for a long time for a baby, and he found out he is sterile. My husband agreed without even speaking to me. I'd agree too, Aven is my twin brother, and I know how much being a dad means to him and I'm all for it! But I don't like how they have pretty much arranged everything and they didn't tell me, but yet my family (Not our parents) & my husbands brother all seem to know........