we've got 4 points and a moment about axis perpendicular to plane of four points at center point of square.Whether I consider two equal & opposite forces in X direction or Z direction it will have same effect of moment.
Kindly let me know whether I should consider the equal & opposite forces in X direction or Z direction.(X & Z are co planar axes in which four points lie).
It's difficult to understand what you are asking. Please consider adding images or files next time and letting us know what software you are using.
If you have a doubly-symmetric structure then applying a load in one direction and the other would not strictly be necessary so long as you design all members for the maximum, envelope forces.