The Shulhan Aruch writes that one who recites Kaddish should bow at five points during the recitation: the first word, "Yitgadal"; "Yeheh Shemeh Rabba"; "Yitbarach"; "Berich Hu"; "Ve'imru Amen" after "Da'amiran Be'alma." Some have the custom to bow also while reciting "Ve'imru Amen" before "Yeheh Shemeh Rabba."
A number of Poskim, including Rav Haim Palachi (Turkey, 1788-1868) and the Kaf Ha'haim Sofer (Rav Yaakob Haim Sofer, Baghdad-Jerusalem, 1870-1939), cite the Yad Aharon as ruling that one should now each time he says the word "Amen" during Kaddish. It is recorded (in the work Neveh Shalom) that this was the custom in Cairo, and this is the position taken by the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Od Yosef Hai. By contrast, the Ish Masliah (Rav Masliah Mazuz, 1911-1971) claimed that this custom has no Halachic basis, and should not be followed. This is the opinion accepted by Hacham David Yosed, in Halacha Berura, writing that one should bow only at the five points mentioned by the Shulhan Aruch.
In contrast to all these views, the Gaon of Vilna (Rav Eliyahu of Vilna, 1720-1797) ruled that one should not bow at all during Kaddish.
The accepted custom among Sepharadim, however, is to bow at the five points mentioned by the Shulhan Aruch, and some bow also while reciting "Ve'imru Amen" before "Yeheh Shemeh Rabba," as mentioned.
It is customary to turn to the sides when reciting the words "Be'hayechon U'b'yomechon." This is done as a sign of affection for the congregation, as these words express the wish that Hashem's Name should be glorified with the coming of Mashiah "in your lives and in your days" – during the lifetime of the members of the congregation.
Summary: Different customs exist when it comes to bowing during the recitation of Kaddish. The accepted custom among Sepharadim is to bow at the five points mentioned by the Shulhan Aruch, and some bow also while reciting "Ve'imru Amen" before "Yeheh Shemeh Rabba."