Trying to figure the best overall odds without using to many battle items for the final battle. Here is the best I have to offer.
Looking at it:
John, Evelyn, Mel,. Wilbur, li Xiu
If your only goal is completion:
Bring Mana pots by the bucketload and along with something to Nerf the attacks.
Fire Wilbur then Mel to rip the spirit link, then use John and Evelyn. They’ll have the defense down and take damage. For 3 turns you should be able to fire tiles at them and be protected from attacks. Fire li Xiu to take their Mana away when you need to.
Wash, rinse repeat on turn 4, using the pots to charge up. Should kill them in no time.