I can do Wyvern 10 now reliably with Ken, Aramintha, Angelica and Luna.
For Wyvern 11 I cant really survive all the attacks, got Krau at 20k hp and Angelica at 17k atm but I think my units are a bit too slow, 120-130 speed on all. Feels like Angelica cant get her heals in fast enough. Might try...