I totally get that is would be convenient for your family, but I personally would say no. I would want to make sure that the focus was on me (That sounds really selfish as I say it, but oh well ). I doubt you guys will end up agreeing on everything, but lets say you do. I would not want people comparing the 2 weddings; who had nicer flowers, better colors, a nicer dress, etc. That is likely to happen if the weddings are only 2 days apart.
In the end, you have to decide if you are willing to share the spotlight during the most important week of your life.