At this time I have about 15 challenges that are not accepted. I don't know the lineup for these challenges anymore, because the most of them are there for a week. Isn't it possible that next to the withdraw challenge link there will be a view link, so you can see which members will play a challenge.
Maybe you can combine this to the equally matched challenge thread, by making this view link available to the other clanleader. Because not all clanleaders want to give their lineup, maybe you could put something in the edit clan link where each clanleader can decide whether they give their lineup or not.
The clanleader of the challenged clan can decide to accept or decline the challenge. If he accepts, he makes his lineup, which the other clanleader can see, if available. The challenge starts when one clanleader clicks the start challenge butten. Maybe it is possible that both clanleaders have to click it, so they both agree with the lineup.
I am not sure I explained it clear, so please reply, and if it is clear, let me know what everybody thinks of it.
Second, I have no idea if this is possible. I don't know anything about making a website and making programs, but it seems not too difficult for me.