The old one is considered to be Grazdan mo Ullhor, mentioned by Missandei in Daenerys VI (though I am not sure how that conjecture was made). So we have:
Grazdan mo Ullhor (or Grazdan (old))
Grazdan (fat one)
Grazdan (tall one) (or Grazdan (spiked beard))
Grazdan, who was not described. As I proposed earlier, the article about him can be named Grazdan (Good Master).