One of my sewing groups just finished a row quilt that was a round robin. The most successful ones (in my opinion) had a multi colored focus fabric in each block. I would suggest if you go with a focus fabric. Decide on an amount for each person. Whether it's a third of a yard or half a yard per person and cut the fabric. Staple to each piece that it's one piece per person. It's amazing how fast fabric disappears when several people work on a project. I requested a red, white, and blue for a Veteran's quilt. Even included a small USA flag just so I was clear about colors. Didn't work. Everyone has a different idea of what works.