Formula that accomplishes the above needs:

   if {CnCnstncy_1.CnCnstncy_1_CodeLong} = "CURRENT PARENT" then    
            {CnRelInd_1PrAl.CnRelInd_1PrAl_Class_of}
   else if {CnCnstncy_1.CnCnstncy_1_CodeLong} = "FACULTY/STAFF" then
     (
       if not isnull({CnPrAl.CnPrAl_Class_of}) and {CnPrAl.CnPrAl_Class_of} <> "" then
            {CnPrAl.CnPrAl_Class_of}
       else
            {CnRelInd_1PrAl.CnRelInd_1PrAl_Class_of}
     )
   else 
      {CnPrAl.CnPrAl_Class_of}