[13lackGu4rd]

what you can do as Vanheim really depends on your pretender choice, and more importantly its paths. if you took an SC Chassis(say 1 of the Titans) than you can equip him as an SC assuming you have const4 or even const6, than fight them. just make sure to equip him with items that will both stop most of their damage(so you won't die easily to a few Adonim) and items that will punch through their defenses(so don't take a fire brand if they have fire immunity via items).

if you took a rainbow pretender, or even the Titan with basic A1E1 and have at least A4 on him than you can forge the air boosters at const4 which will allow your Vanjarls(which you should have a lot of, recruited from every non capital fort all the time) to spam thunderstrikes like madmen and not run into too many fatigue problems(thanks to having high enough level in air magic compared to the required 3 for thunderstrike). this will require a lot of air gems though, so that would really be the limit on how many such long lasting Vanjarls you can have.

another option is to research to mass flight and weapons of sharpness ASAP than recruit a huge amount of Skinshifters and go to war. with mass flight you close the distance to the Adonim very fast, before they can finish putting up all their buffs, and with a few weapons of sharpness casters, you can cover most of your Skinshifters. so you need enough casters cast on turn 1: mass flight(once) and weapons of sharpness(a few times, depends on how many Skinshifters you brought. give your Skinshifters orders to attack rear, (spell casting will happen before regular troop movement, so they'll all be buffed before getting face to face with the Adonim), instead of a more typical hold and attack order which lets the Adonim get most of their buffs up.

as for your allies, Ermor can reanimate massive undead armies and can skelli spam during combat with his mages, so I really don't see a problem for him... he also has access to Shadow Blasts(with penetration boosters, very devastating for Adonim) and other death goodies(even Disintegrate if high enough research). oh and he should have access to the acid spells too IIRC. no armor(acid rain IIRC) and massive undead hordes=dead Adonim...

Shinuyama has good access to most magic paths, including acid spells IIRC, so they can bring the to fight whatever the Adonim are vulnerable to. rely heavily on summonable armies(drakes, snakes, lions, etc) and whatever combat spells that will hurt the Adonim(depending on their equipment).