When were you expected to arrive and when did you tell them you would be there? Why is it important to you to have a group of people who all want to do the same thing at the same time? Why not seek out individual friendships? It sounds like you and C don't have a lot in common and you don't like C. But they do. That can happen in groups of course.
Group dynamics can change especially if one person's lifestyle is changing. I had friends who were unwilling to accommodate my new schedule when I had a baby, and who were unwilling to make only tentative plans when I worked very long and unpredictable hours from age 28-42. I had acquaintance groups. Monthly dinner/networking group, monthly book club meeting, like that but mostly I made plans one on one, or with other couples, or sometimes with 2 friends. If it's that important for you to have a "group" then accept that that is often harder to find -as you're seeing now in a group dynamic that is not working for you.