I think (?) you can only get that many souls with VIP bonuses (i.e. $$$ spent). (Or can you get there with a third necromancy traited character, such as KoS??)
Excluding VIP bonuses…I think the most you can get is 130 per battle (with Celestial Armour & Warlord IV difficulty).
For an easier choice, go for Warlord I (100 souls), Warlord II (110 souls) or Warlord III (120 souls).
Serpent/Griffon Rider, Valkyrie, Valkyrie, Druid is a solid team for re-completing challenges. First level of Khetar & Khaziel are pretty straight forward, particularly when the traits are considered.