Is there any way we can create various roles within a group?

As previous commentors have already suggested, and to clarify: Appian has fully flexible group-of-groups functionality, nested to an arbitrary number of levels (i.e. a large hierarchy is possible), so almost all "roles" use cases should be solvable by making a separate group for each needed role, categorizing those into larger groups as appropriate, etc.

As previous commentors have already suggested, and to clarify: Appian has fully flexible group-of-groups functionality, nested to an arbitrary number of levels (i.e. a large hierarchy is possible), so almost all "roles" use cases should be solvable by making a separate group for each needed role, categorizing those into larger groups as appropriate, etc.