Can anybody give me some advice on how to beat King Desius and his group that seem to keep on coming. I can not even get the Kings life down much at all?

I don't remember Desius having any allies in his battle?

anyway
1: did you successfully activate the seals while going through the tomb?

2. looking at your team, a major issue is the team setup
Bella I assume is Shadow Tank/slot 1?
Shadow is a Magic/Int element, and as tank it generally uses Int/Agi-focused equipment (Illusionist, in non-lg gear) for the highest hp absorbtion (higher damage = inflicted debuffs do more), defence and evasion.
As it is, three of her equips, including the relic*, are Str-focused (Myrmidon relic, assassin armor, assassin bracelet)

(*Relics getting called out more directly because relics give an additional bonus to whichever Damage stat they're aligned with, which can be the difference of tens to hundreds of points depending on level)

Wise Guy I assume water buffer?
Water is Physical/str element, and as a buffer would use Assassin (str/agi) and/or Myrmidon (str/dex) based on player preference and pet needs.
He has Int-based Relic and bracelet

Bowan Air attacker
Air's another Physical/str element. Focus should be Str/Dex (Myrmidon gear) for best output (the attacker elements, air and fire, rely on crits to inflict their debuffs, and obviously also to deal as much damage as they can as fast as they can).
Another case of wrong relic type for element (disciple gear's generic placeholder stuff, so it's like, fine-ish)

Thank you