I feel like the last one was a bit mistranslated, or at least translated in a misleading way. I highly doubt that's actually Miku's younger sister, more likely she used "oneesama" in the yuri sense, i. e., she wants Miku to be her top.
Just being a regular well behaved dude was all that was needed to almost make an entire class fold...the absolute state of the male population of that world lol