We would have different times to have different matches.
Eg. We fight in 3 mods; Wushu, Aikido and Judo.
We all nominate a few members to fight in those mods, and the other clan would do the same.
A time would be scheduled for that fight, and if one player doesn't show up they have one more chance. If they miss the next one, it is counted as a loss.
At the end the wins will be counted up, presenting the winning clan.
A replay must be showed to prove your win, and then it can be verified.
I basically answered your question plus more.