At first, Z'ant is the queen of al T'rangs..like Yamir is for Umpani and if you want to work for T'rangs you must speak to him very often.
If the guards attack you you are hostile to the T'rang and Z*ant also attacks you. He is very hard but with magic screen and element shield you should manage it.
Normally the T'rangs are not hostile if you arrive at Marten's Bluff the first time; you must have attacked a T'rang somewhere else before, perhaps you killed Tantris in the mines.
They are not hostile as long as you are not hostile
It has nothing to do if you have been to upper MArtens Bluff before but if you have killed T*Rangs
Try your luck
Niob