Dear Rabbi When saying kaddish on the yahrzeit for a family member (non parent) e.g grandparent, does one need to say all the Kaddashim at shacharit or does just one need to say just kaddish drabban and one standard kaddish?

ב"ה Shalom First of all, if both of your parents are alive, you should ask permission from them to say Kaddish for the grandparent. Rav Shlom Zalman Oirbach zt"l wrote that if both parents are alive, he should refrain in any case. (הליכות שלמה תפילה פרק יא:טו ) There are essentially two Kaddish Yatom=mourner's Kaddish at Shacharit. One after Aleinu and one after Shir Shel Yom. The Kaddish D'rabbanan is not a mourner's kaddish, and it should be said even if there is no mourner in the Bet Knesset. However, usually the custom is that where there is an Avel already saying Kaddish, that he says the Kaddish d'rabbanan as well. In regard to saying Kaddish for a grandparent, the Magen Avraham (132:2) quotes the Rema in his responsa, that if there is a grandchild saying kaddish in a place where there are actual Avelim for a parent, they should have preference over the grandchild and say two Kaddishim, while the grandson should say only one Kaddish. However, this is only relevant in a place when not all the Avelim said Kaddish at once but not where the Kaddishim are divided among the Avelim. This, according to Rav Moshe Feinstein zt"l, is unlike today when in most places, all the Avelim say kaddish. (אגרות משה יור"ד ח"א סי' רנ"ד) Therefore, if you took upon yourself to say Kaddish for a grandparent, all the Kaddishim should be said. Besorot Tovot and Happy Purim