For Clan boss I do run Draco, Siphi, Skullcrusher, Tayrel, Kael and Bulwark at the moment.
I do have trouble going past Spider 10 but I do have Galek to gear up, Doompriest and Lua with the classic Armiger coming in.
Rest I haven't tried much to be honest.
I would prioritise Arena altough to improve my Great Hall but it seems I can't go Bronze 4/Silver 1 at the moment, everyone running Shield sets and there's a lot of inactive people dropping ranks that do not facilitate the situation.
All your 6stars are attack champs...that is your problem. You need to farm chickens, lots of chickens... amazing roster of champs.
siphi, skullcrusher (minimal books for cooldown), tayrel, uugo, umbrall, zelotah (no books needed), jarl, doompriest (no books needed) , lua, narma
I would not open another shard until all those are 6star...