so after reading some rough translation if I understand that right it seems like someone is starting to be jealous and showing signs of possessiveness (yeah I'm looking at you Mei you Tsundere)
So they actually thought about their future more like Yuzu thought about it internally that as long as they're sister there's more chance of them being together than as a lover would and as a family they could be together forever, so she think that would be better with a big question mark?
but then Matsuri ask the crucial question I hope Yuzu get that in her head or this villain purpose will be for nothing, I mean this is the only time I kinda agree with Matsuri, if you love someone isn't that you want to make love with them that if you don't have any desire or what so ever it could be just friendship, but I think Yuzu knows the answer she just won't admit it yet.
As for Mei Idk I think she still regards being family more important than any romantic love or so she think so but maybe after this she would finally realize that what she feels for Yuzu is far from being family, or rather she already knew it she just won't admit it and nice excuse MeiMei I never heard about a sister kissing her onee chan's nape as a quality time as being sisters all of those action you did just makes me sure you want Yuzu so bad.