What are the reasons for one to stand during Kaddish Shalem and Chatzi Kaddish? Does one just need to stand if he or she is already standing for another reason already? Are there only specific parts of the Kaddishes that we are required to stand for?

The Ramah writes (Orach Chayim 56): There is a Minhag to stand for anything defined as a 'Davar Shebikdusha' (somthing with a certain level of holiness) and the Mishna Brura (Ibid) derived from Eglon, the Moavite king, if he stood up to hear Hashem's word, we shood stand for a 'Davar Shebikdusha'. Of course, if one is already standing he shood remain standing. One should stand until after Amen Yehe Shme... and some people are Machmir to stand until the words Da'amiran Be'alma, and by this subject, it is better to be Machmir (Mishna Berura, Ibid). This is the place to mention that the Spharadi Minhag is not to stand up for Kaddish, but if the Kaddish caught one standing, he should remain standing. Rabbi Ro'i Margalit