In Star Wars, do we know who Rey's grandmother is? Or do we at least know when Rey's father was born? Was it before the events of Revenge of the Sith or after?
UPDATE: The Rise of Skywalker Novelization was released early to a select few and as such, new information is finally coming out to help shed some light on all of the details, including Rey's lineage.
As it turns out, she has NO GRANDMOTHER. Her father was a partial clone of Sidious, whose vessel was deemed "imperfect" and "powerless" by The Sith Eternal, who were trying to find the right body for Sidious' conscious...
Paraphrased by Screen Rant
This passage in the book reveals after Return of the Jedi, Palpatine "thrust his consciousness" into a clone body. However, "the transfer was imperfect" and members of the Sith Eternal worked tirelessly to engineer a new vessel for Palpatine's essence. One of these attempts is described as "a useless, powerless failure" who was "a not-quite-identical clone." While this body wasn't fit to house Palpatine's power, it was still able to live and eventually became Rey's father.**
It's currently unknown, but likley will be answered in more detail at some point. These are some likely places where that might happen.
- Rey Spin-off: The Rise of Skywalker does set-up a potential spin-off with Rey & Finn starting a New Jedi Order (much like Luke did in the former EU). By choosing to make Rey a Palapatine reborn a Skywalker, is very symbolic to the idea that she takes the baggage of The Skywalker Saga and her new-found family history with her. This was also part of the lesson Luke imparts on Rey, reminding her that age alone does not prevent one from having their identity be re-contested or that the past simply dies.
- The Rise of Skywalker Novelization (Expanded Edition) - This book is coming out soon and it may shed more light on who Rey's parents and grandparents were, as the Force flashback sequences could be extended.
- It's rumored that Star Wars is about to go the way of Marvel's MCU. Next Monday "Project Luminous" is officially debuting as a multi-book and comic book series that *may lead into the next film (2022) or series of films reportedly set in The High Republic Era. Without giving some possible spoilers away, all I will say is that this takes place in unknown regions and because of the MCU factor and given other loose elements still blowing in the wind (Ashoka Tano, The World Between Worlds, The Child, The true nature of Palpatine's return, etc), it might be possible that Rey's grandmother's lineage could come from this era/series and begin to tie-into other future works.
- Disney+ Spin-off Film/mini-series. While there hasn't been any talk of Palpatine/Sidious series explicitly, there has been talk of an Anakin Skywalker/Darth Vader story of sorts. If there was such a series taking place any time after Revenge of the Sith, that might be a way to also reveal Rey's grandmother.
- Other Books and Comics.
Most likely no one. The twist in the third movie was out of nowhere so it's most likely not planned at all. And in the second movie we even had the twist that her parents were nothing special at all.
So if the comics will make any work from this adaptation then they will most likely create a new character to be her grand mother, or a throw away side character.
While it is not revealed in the movie, the official novelization indicates that as part of his contingency, Palpatine prepared a clone before being thrown down the Death Star II shaft by Vader as he sensed the flicker of light within the latter. Before his body hit the ground, he had learned to project his essence into one of the Clones. This was an imperfect clone. Palpatine's son (Rey's father) is also a clone. The son is one of the clone projects of Palpatine because they kept trying to make a body for him to contain his power. The son is a perfect bodied clone. Palpatine hated the son for being a failure as he had no Force abilities. Note: the novel itself has not been released yet and many revelations that are being reported are only available as "leaks".