Q. Dear Rabbi Bartfeld, My father was Niftar (perished) when I was young.  He himself wasn’t frum nor did he grow up frum, but he did have traditional Jewish values, and was known for his humility and Middos Tovos.  I am careful to be mechabed (honor) his Yahrtzeit in accordance with minhagei Yisroel, i.e. learning Mishnayos, making a tikun, etc.).  
I wanted to know what my chiyuv (obligation) is for my extended family (i.e. grandparents) yahrtzeits.  Should I be saying kaddish, and observing their yahrtzeitin with learning Mishnayos and making tikkunim? 
On the one hand, it is very unlikely anyone else will be saying kaddish for them, as I am one of the few Shomre Torah Umitzvos einekelach.  On the other hand, I harbor resentment at their lack of kiyum of Torah and mitzvos, and therefore why should I take upon this achrayos (both time and financial).  Perhaps I should learn from Chizkiyahu and not be mechabed elterin who did not walk in the ways of HaShem; at least this way they won’t be able to “oseh ma’ase k’zimri umvakesh schar k’pinchas. (demand rewards for wrongs done)”
Kindly let me know da’as Gedolei Torah on this matter
A. Horav Shlomo Miller’s Shlit’a opinion is that it is correct to learn Mishnayos in their name, simply as Hakaras Hatov and giving thanks, since after all you as a descendant likely benefited in various ways from their efforts, even if they were not intended. Therefore, thanks should always be given and no better way to do so, than to be merit them with the mitzva of learning Torah.
According to the Rov, grandchildren do not recite Kaddish for their grandparents on their Yortzait. However, there are different traditions when there is no else to  recite for them.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller, Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a