A must see Torah Temimah [TT] on Vayigash. Here, the TT presents an encapsulated resource book on the issue of honoring grandparents
See TT Vayigash 46:1
The upper text quotes the Midrash Rabbah [MR] Stating Kibbud Av trumps kibbud Avi Aviv
[Literally paternal grandfather]
The Rema in Yoreh Deiah 240:24 deduces here that we see kibbud Avi Aviv is at least in the discussion it is therefore an obligation albeit a lesser one.
In note 1 below the line, the TT says the following:
• Rema rejects Mahari Kolon who sees zero obligation
• The GRA rejects kibbud Avi Imo [Maternal Grandfather]
thereby taking this MR very literally
• The TT suggests that the Bavli would disagree with this MR and leaves the GRA in "Tsarich Iyyun" status
•. He quotes several Bavlis and an interesting Rif and Rambam about miracles that occur to one's grandparents [or ancestors in general]
Quite a breadth of sources!
This might give us a brand-new research topic for Parshat Vayigash