Referees::__pkRefereeID = Tests::_fkRefereeID
Referees::__pkRefereeID = Assessments::_fkRefereeID
A check box field in Referees can identify which Referees are instructors and which are assessors. (I assume a referee can be both.)
"Pulled out with sorts" seems a bit vague. I think you mean that you need to be able to pull up lists of Instructor Referees and Lists of Assessor Referees. this can be done by performing finds--either manually or in scripts. A relationship or a filtered portal can also be used to list Referees of a specified type.
InstructingReferee::__pkRefereeID = RefereeClasses::_fkInstructorID
ReferringReferee::__pkRefereeID = RefereeClasses::_fkReferreeingReferreeID
For an explanation of my notation, see the first post of:Common Forum Relationship and Field Notations Explained
Referees, InstructingReferee and ReferringReferee are all Tutorial: What are Table Occurrences? that refer to the same data source table.