This is possible to do by creating Groups in Workfront proof. From the Proof admin area, go to "Groups" in the left-hand panel. Then create a group and add all of the users and their associated proof roles. You will then be able to add this group to a proof approval stage in the future, and all of the people within that group will be added with the roles you configured.
You can read more on how to configure and use proof groups here on Experience League