My thoughts on the sisters. Probably nothing new, at least for the first part.
It is a yuri manga so who knows where it might go, but just based on the six English chapters, I'd say Sakura loves her sister/playmate, but in a normal sisterly way. Ashima's actions could be part acting out her reputation, partly unsettling/driving away Sakura, maybe part getting some contact with one of two people she can touch. Sakura doesn't like it and genuinely protests but doesn't view it as a dealbreaker yet, especially with guilt for how her parents treat Ashima. I imagine thoughts like "If tolerating aggressive footsie is what it takes to keep Ashima around, I'll tolerate it."
Spanish chapters: Notably, a naked bath scene with them has no sexual tension whatsoever. After they reconcile we don't see Ashima do anything improper. There's also a flashback of "I was taking my frustrations out on Sakura." We do get the cliffhanger-proximity marriage question, but I think Ashima asks more because she's wondering about Rin's future, and Sakura's reply of choosing Ashima over marriage could just be a middle schooler who has yet to feel lust or fall in love and thus can't really imagine what she's rejecting. From what we've seen I don't think Sakura's really discovered sex yet; Ashima at least thinks about it, though we don't have a solid attraction yet for her either.
Of course, that's the realistic take on the text. Given the metatext that the author chose to put that in a yuri manga, in a short chapter where the MC kisses her love interest, incest fans can still hope.
Totally unrelatedly, I wonder if Chekov's Death By Ocean is on the wall. We've had (tiny spoiler) two different "don't kill yourself!" reactions to someone looking at or standing in the water.