Get more 60s.

For fk: apo, armiger, udk, elhain, jorrg.

Greatly appreciated, thank you! Farming food at the moment, got an armiger on the day you replied and received another once since so used to book him. Just got 3* blessing for jorrg which will help too so I've ascended him since and will start to put more time and resources into farming to break pleateu ☺️

I would build up Fellhound and Soulbond for FK as well.  Would not use UDK there, he will be great for Dragon and Ice Golem and Spider.  

Soulbond can also help on spider. 

Apothecary can help a lot in many cases.

Frozen Banshee  can help on Dragon (and CB) as well.  I do see the makings of a decent CB team with Fayne, Frozen Banshee, Geomancer, UDK, Anax, Renegade etc.   I would focus on CB next, because the resources you will get there will help you more.  Lots of ways to go there.

Scarab king is tough and you will probably need a team of 60s and 50s to beat him.  From what you have Armiger, High Khatun, Soulbond will help and probably need 2 more AoE shield champions on shield sets.  Metalshaper, Draconis, Scrapper are all rares who can do this.  But all of them have to be build.

That said, you next priorities should probably be getting Geomancer and UDK to 60.  I would not put any more resources on Warpriest and start replacing her with Apothecary in non FW content. 

Good luck!

I suggested UDK for the FK team for one main reason - he makes it far more likely you reach the boss alive. The goal here is not to clear waves as fast as possible.