I don't think it's a good idea that Miu will declare war against Ayako for Takumi. Ayako surely lacks confidence and will definitely back off to make the younger ones happy... and it really seems like Miu likes Takumi too.. sheesh...
I love this type romance. If anyone knows more like this please share with me. I hate ntr, incest and child abuse types (shots, loli). I respect homosexuality and bisexuality but I'm prefer straight. Please share with me your knowledge, thanks.
While not similar to this it matches all of your criteria:
https://mangadex.org/title/50385/while-cross-dressing-i-was-hit-on-by-a-handsome-guy/chapters/