Kyou and Eri's relationship was over after the fight at the movie filming place. It took them a month and there best friend dragging them to a festival. Then set up time for them to talk for them to finally spell it out to each other.
We can be reasonable sure Sayaka lied about some thing memory loss, brain damage, that not being Hikari and giving birth. We can only say this because we have contexts that Kurumi is lacking. I wonder how much more half truths and lies she told.