Im at 4 dudes now and just tried the desert boss, he does two attacks at once and I cant keep up with the healing required. Plus he put serena to sleep one turn and that was just instant GG - only got veroinca to dispel it and you have to wait for her turn obviously and by then its too late
Im at like level 16 for hero/eric and 15 for veronica/serena. Will grind them another extra level or two and try again. Seem to need to grind a lot though before bosses. Which is cool I like the challenge, but when its one shotting you and you cant heal the difference at all its a bit much