At the start of the week there were 27 members in our clan, but the next day there were only 24. Can we compete in the Most Disciplined category?

When calculating a clan’s discipline, only quests completed by a clan with 26+ players are counted. In this case, assuming your clan completed at least two quests on the day it had 27 members, it will be eligible for the Most Disciplined category. However, only quests completed on this day will count toward your clan’s score.