Finally finished this after unlocking it weeks ago. Most of the quests are relatively easy without needing any higher rarity servants. The only exception is the last one which apparently is doable with double Mash and Euryale but I had problem making it work with the closest one being Euryale, Mash, and Andersen. Except Andersen died pretty early and replaced by backup Merlin and the screenshot above is the end result (Merlin died one or two turns before).