I'm having 2 MOHs!!! I think it's a good idea.

I agree that if you really want to have them both, then have them both. Explain to each of them why you chose to have two MOH. I would then make a list of what you want each one to do. Make sure you aren't giving your friend all of the "big" things and leaving his sister with all small things. Evenly divide the tasks and everything should be fine.

This is an old post but thought I would respond. I am having to matron of honors. One is my best friend since I was 12 and the other is my sister in law. I was maid of honor in both of their weddings. But I really didn't want to choose between them because I love them both. And I really didn't want to pick one or the other. They are going to share the duties. And I am not having any bridesmaids. My fiancee is have two best men also. His best friend and my brother. My brother is actually the way I met my fiancee. And they are actually best friends now. So, I personally think you can have two. Why not? It's your wedding!