Just a sugjestion: for a clan tourney
If 8 or more: simple tree/bracket style play. The ones who applied earlier get the free passes, such as a 10 clan tourney: last four to apply get 1v1 so it turns into a simple 8 bracket.
If below 8 do round robin, you face every other entered clan once for X rounds each.
After, count up the won and lost rounds to find the winner