These various branching events make sense to me as you've stated them. One reason I also think they might work is, Perry says they could spend "one or two weeks" in August at the beach house (and these two weeks might easily correspond to Chapters 12 & 13) and then the beach house would end, the Wildcats shoot would end, and Eva would be able to bring all the branches back together for the end of August or start of September back in Baluart. Obviously relationships between characters would be different based on what had happened in August, but the default situation for everyone would be back to "normal" life and events (the MMA tourney, Ian's writing contest, Lena working in the cafe, etc.) at the same time.
One thing we do need to keep in mind, though, is that Ian and Lena won't be at the beach house/Wildcats shoot for the entire chapters. When Perry invites Ian, he says "Sure, I guess... I'm working, but I can take a few days off to go on vacation or something." And when Perry invites Lena, she says "I'd like to tag along too, if I can. Things are a bit chaotic right now and I'm not sure how free I'll be next month." So they will both be going back and forth to some extent between Baluart and the beach. This probably frees Eva a bit in terms of getting in additional content depending on play choices (e.g. Minerva for Ian, Mike or Robert for Lena) but also may mean Ian and Lena might be able to partake in both beach options, on different weeks. Which could be fascinating, as it expands opportunities further.