I think assuming the party can even make its way to the cave in the first place might be too big an assumption.
Given that Aho is both the reincarnation of Diogenes and the living testament of an int-1, strength-10 Fallout 2 build, I don't think its a matter of making way to the cave so much as not destroying the cave.
Could be a strong team. Yoshiko has good wilderness skills, Akko gets decent at magic...eventually, and Mordred is strong. I feel like main issue is lack of leadership and coordination among the members.