The ni' prefix on the House name denotes one of the seven Great Houses. Julia ni'Tamra. Donna ni'Tarak. Kieran ni'Narsan.
It does not denote the rank within the House. Other people in the House, non-Kithrayna, have the same prefix. Victor ni'Narsan. John ni'Tarak.
What the lack of the ni' prefix denotes is membership in one of the lesser Houses. Examples being Alexander Telenias. Kelly Tallart. Joseph Keleyn.
This is the sort of thing that'll go on the inside front cover of the comic or TPB, as there's really no smooth way to explain it within the text until way into Volume I; you don't Need To Know, but it probably helps.