In the camps, Wiesel must struggle to stay alive and to remain human. In your own opinion, how well does he succeed with his struggles?

I don't really know if he succeeds. The reason is it would have been nearly impossible for anyone, no matter how strong, to stay human (whatever that might mean). The whole point of these places was to destroy the soul and that they did. Coming out alive was the best one could hope for. Elie encounters countless atrocities and experiences Hell on earth. His previous iron faith in God had changed and his sense that humanity even exists is challenged. I think Elie is successful in getting out alive. As for keeping humanity, that is a very nebulous concept.