This chapter was really hard in maddening mode, I managed to beat it but lost Mercedes(Priest or Bishop?), Annette(Dancer) and Gilbert. With afterthought, maybe I could save Mercedes and Annette by letting them stand together against the wall, thus only two enemies could attack them at the same time, with some luck maybe they could survive but I'm not confident. I let Dimitri hide in the tree and Byleth(Enlightened One) stand next to him against the wall so also only two units could come in and attack, then I could kill them one by one. Gilbert's fate was indifferent to me so I just let him die, but I was really happy Ashe(archer or sniper?) survived by luck. After clearing this block of enemies, the rest is a piece of cake.