With regards to the third realm did Frege believe that it actually existed and held metaphysical/ontological significance as some people have argued otherwise such as in here:
 http://www.indiana.edu/~jcw1/Realism%20bei%20Frege.pdf
or here: 
http://www.academia.edu/10351788/Demythologizing_the_Third_Realm_Frege_on_Grasping_Thoughts