I don't know what to wear to my brother's wedding?

Hi, I'm a nonbinary trans girl and I'm not out to most of my family. My brother has a wedding coming up in a couple weeks and I've been putting off planning for it, I don't know what to wear, I just want something that isn't masculine but also won't make my family think I've lost my mind. Does anyone have any recommendations? It's business casual btw.