In writing an argumentative essay, it is important to have a strong thesis that connects directly with the evidence provided in the text or texts. When basing the essay on two works, try to find specific points that are addressed in both of them. Those shared elements will provide the relevant evidence from which to develop your thesis. Another way of saying this is to identify the important components first, and then write a thesis that fits the evidence. This approach is preferable to drafting a thesis statement that is very broad or abstract and which might turn out not to have adequate support from the texts.
The draft thesis that you have included in the question is very pertinent to both Night and The Cage. It is also a general statement about how people behave in extreme situations, so it could apply equally well to a wide variety of other literary works. A thesis that works well for these two works will include some general characteristics, but it will also be grounded in specific points that the authors make about their particular situation. Because both authors are writing not just about the Holocaust but specifically about their experiences in Auschwitz, be sure to connect to some concrete observations they are making. Survival, for all the prisoners, was always grounded in their daily reality but also connected to the larger moral and ethical dilemmas about which you are writing.
Two of their immediate, concrete concerns were food and clothing. You have included the example of Elie’s guilt over sharing food with, or withholding it from, his father. Using an comparable example about food in The Cage would strength the point you are making. Similarly, the question of clothing and nudity related to dignity arises in The Cage, in regard to the dehumanizing effect of being stripped. Did subsequent interactions with other people, related to her physical self, help her regain her sense of humanity? You might look for comparable examples about bodily attitudes in Night.
In your post, you mention that you wish to support two different sides of your main argument. This can be done effectively, but as a matter of procedure, you will probably find it useful to work through one side of the argument first, then develop the counter arguments. Going back and forth during the course of your writing may cause you to lose track of the nuances of each side. A practical method for drafting your essay could be to create two lists in two parallel columns. In one column, write out every item you think belongs on one side of the argument, and in the second column, write the countering proposition. It will probably go faster if you do this for each work separately, adding similar information for the second work below the first entry. When complete, your dual-column list will facilitate your review of all the points you want to make; as needed, you can then reorganize them, group them into larger points, or eliminate those that seem minor or too difficult to develop in the space available.