Challenge 3 Done; Curb. Stomp.
Team: Ozy, Chloe, Support Merlin, Mash
Ozy's only real role is to get rid of the Sphinx on the 2nd wave, once it's gone swap him for Mash.
Chloe then one-shots the first Break bar, one-shots the second with a little help from Merlin, and finally takes out the Queen of Abs in a couple of turns. After that, it's just mopping up the mobs.
edit-
Challenge 4 done.
Team: Summer Scathach, Shuten, Support Jeanne, Mash, LAltria, Scathach
Have the Assassins deal with the mobs, both NP'ing the giant boars at wave 3. Then swap the Scathachs.