Should a grandson say Kaddish and Daven for the Amud on the Yahrzeit of a grandparent?[1]

Kaddish: If the deceased did not leave a son to say Kaddish for him then a grandson, whether of the son or daughter, is to say Kaddish on his behalf.[2] This however is only allowed if the grandson does not have any parents, or his parents are Mochel and allow him to say Kaddish for the grandfather. If, however, his father or mother is Makpid, he may not say it.[3] If both parents are alive many are accustomed not to say Kaddish even if both parents are Mochel.[4]

Davening for Amud:[5] If the deceased did not leave a son to lead the Amud, then a grandson, whether of the son or daughter is to Daven as Chazan on his behalf. This applies even if the grandson cannot say Kaddish for his grandfather being that his parents are alive.

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[1] See Toras Menachem 3:7

[2] Mateh Ephraim 3:4; Nitei Gavriel 70:12; So rule regarding Kaddish during the first year: Shut Rama 118, brought in M”A 132:2; Kneses Hagedola 403, brought in Kaf Hachaim 55:28; Beir Heiytiv 132:5; Beis Lechem Yehuda 376; Beis Hillel 376; Teshuvah Meahava 1:17, brought in Pischeiy Teshuvah 376:7 [See there for the details of Kadima for a grandson]; Gilyon Maharsha 376; Peri Hasadeh 92; Igros Kodesh 12:196 [printed in Shulchan Menachem 5:296]

[3] See Teshuvas Harama ibid; Beis Lechem Yehuda 376

Other opinions: Some Poskim rule a mother cannot protest the son saying Kaddish for his father’s father. [Teshuvas Shaiy, brought in Beis Lechem Yehuda ibid]

[4] See sources in Chapter 26 Halacha 2

[5] Peri Hasadeh 92 regarding the year of Aveilus; Nitei Gavriel 70:12; Toras Menachem 3:7 that the Rebbe Rashab Davened for the Amud on the Yahrzeit of the Tzemach Tzedek and the Rebbe Rayatz Davened for the Amud on the Yahrzeit of the Rebbe Maharash