I did a few runs just now. Expert red hits hard single-target. It seems soloable, though I think I had one other person. Expert blue does an AoE with poison as a spammable special that does about 1.5k damage with attack debuffs applied. This is very nasty if you get attacked with it repeatedly. That said, with my triple healer team I soloed a fight from 60% HP to 0 without losing anyone, so soloing the whole fight could be possible. Bring a healer that can remove status effects, strong healing (at least two healers that can heal for 1200+ each), and strong attack debuffs or you're going to run into trouble.