You can use both anywhere....without knowing the composition of your other champions, this question is hard to answer. Which of the skill you do not have in your teams so far? 

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.

I would go with Tayrel because you said your using Tayrel on your Clan Bosss team.

need to see screenshot of roster and know who is 60 and who is already booked

Sorry for the delay, I've attacched few SS of my pool and vault.

No Books in any of the champs a part from Kael, Siphi, Elhain and 1 in Draco. 

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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...

6 star and ascend skull crusher first and book his a2. Tayrel is great and essential in many areas untill you get better champs ( which there aren't many ) but books on skullcrusher are the difference between mediocre and amazing.