If Rey killed her parents, Kylo should’ve really revealed it in TLJ. God, imagine Rey’s reaction then. She probably would’ve joined him. So another parental reveal just feels sort of redundant. At this point I think it could be better to focus on her future, rather than her past.
I think the idea is that Palpatine revealed to Kylo Rey’s dark nature, her place in the Sith Dyad and her unfortunate past.