I'm still pretty sure Silver left the council >>
Also Genny, while it may be too easy, you don't want something too difficult. This is about the beast be redistributed in a fair way and relatively quick way, nothing to do with difficulty.
As for solutions, you could do multiple things, it need not be all in one. You guys can have gm's play the role as rampaging biju, you can probably even have Genny run a tournament for a biju or two. You could do Naruto trivia, hell you could put everyone who wants a biju names in a hat and draw for all I care.
It just has to be fair, whatever happens. You guys should def not accepts challenges though. That for one is a mess, as there aren't many of you to take over defending 0-3 and 5-9 at the same time.
Also are there even that many people to redistribute them too? I see only Madara, and Athos as def, with maybe Shadow and T'Challa possibly wanting in. If you somehow get lucky and only have 9 or 10 people, could host a tournament where placing in said tournament determines your biju. In a 9 person tournament, last place gets the 0 tails, etc. Anyway, I trust you guys, just throwing some opinions out there. You guys shouldn't sweat this too much. One they are redistributed, anyone can challenge for what they want anyway.