For the stage 4b with the mini Xanoses: I passed it with Lingling, Jasmine, Sylphi, Taurus, Goram at level 95, all heroes O+1. Lingling and Jasmine do the healing, Jasmine, Taurus, and Goram interrupt, Sylphi does the damage. Taurus is really surprisingly good for that stage. Auto battle won't work though since the interrupts are crucial.
For the first stage, I can't remember my team exactly, but I remember that lifesteal / healing is more important than having a large amount of health. Sylphi and Goram will do wonders. I also hear that Glacia / awakened Valan are a great combo for chapters 17/18 and of course Batman is a great help if you have him.