If both sisters were actively dere to the MC, there would probably be no blood left for his brain to study.
Besides, big sis said last chapter she's fine being sandwiched between MC and lil sis.
Excellent chapter(s), as usual. The art is always so good.
I do wish we could have seen more of Yui-nee and Enami interacting since we've only gotten vague details on their past relationship so far.