I'm so sorry to hear about the accident... that's so hard! At one of my best friends weddings, the only brother of the groom, and his dad had passed away, and the mom carried 2 roses down the isle to represent each of them. I thought it was very tasteful, appropriate and sweet. Could the groomsmen brother stand with yall, so it won't be uneven, and maybe have a special boutonniere to honor him? It is your day, but I also feel that if each of you only had 2 attendants each, that both of his must be very close and pretty important. So when you look at your pictures later on down the line, you will always see something representing your FI's best friend. Just a thought. Again, I'm so sorry yall are having to go through this right now. Let me know if I can do anything at all to help!