Is there an obligation to give respect (in the form of physical provision) to a grandparent whose child, your parent, died? For example, if Ruvein has Shimon and Shimon has Levi, and Shimon dies, is Levi obligated to give respect to Ruvein?
I ask this from a gemara in Sotah (daf mem-tes amud alef) where it says a story of Rav Acha bar Yaakov who raised his grandson Rav Yaakov and then when Rav Yaakov got older he was asked by Rav Acha bar Yaakov to get him some water; he didn't and said, I'm only your grandson. And (I assume) the reason Rav Acha bar Yaakov raised him was that his child was no longer living.