See if I understand what you want to do.
You want to have a taxonomy called “Staff”. To this taxonomy you add each staff member as a term. When editing each staff member in this taxonomy there is another taxonomy field that lets you select terms from the “Roles” taxonomy.
Next step is to set up multiple taxonomy fields on the “Project” CPT. This taxonomy field lets you select terms from the “Staff” taxonomy that have a specific role selected in the “Role” taxonomy.
