When Eiji dumped Spoiled-chan and professed love and faith to Rin, the resulting shock served as in 'impetus' for the 'personalities' to emerge and gain self-consciousness. The vessel we know as 'Rin' activated a defense mechanism unknown to anyone in order to protect the 'existence' of...
It's pretty much confirmed that Rena is the mother. I think the fake 'Rena' is Itsuki tho, because she's the one with the secrets and the one who's most attached to their mother (can be seen in earlier chapters).
About kiss:
Nino is most likely to use underhanded techniques to gain upperhand...
Yuuka won't ever be alone now. Heck, they could even possibly 'wake up' the other metanoids. BUT she's the only actinoid. Which means that several years from now, she'll inevitably die and leave shiro to enjoy his harem (and the world will only have machines unless they somehow create artificial...
they should change miku's headset next chapter or make a chapter where fuutarou chooses one for her (CAUSE SHE FREAKING JUMPED IN THE RIVER WITH IT. no way it still works perfectly)