Hello. 1. You can do it without any problem. Inability to use together in this case only in the same formula This will cause the problem of sedimentation of the substance. but if you continue to apply the skin in each formula No problem 2. No problem 3.
Azelaic Acid focuses on acne/oily skin/whiteness while
Tranexamic Acid will focus on the white / reduce melasma only. only