what do you call sex with mother and two sisters?
Well, sex with Mother-Daughter duo is called "Oyakodon" (aka., Parent-Child Bowl), while sex with Sister-Sister duo is called "Shimaidon" (aka., Older-Younger Sisters Bowl).
But there is no specific word for a Foursome like that.
Maybe, we can call it "Oya-Ni-Ko-don", aka., Parent-Two-Child Bowl.
"Ni-ko", sounds similar to "Niku" which means Meat.
I mean the slang Oyakodon is basically the name of the Japanese food which is described by "bowl of rice topped with chicken and egg".
anyways their mother gonna want his children later soooooooo…..
foursome!
Well,
not really.
As per the Web Novel,
the Mother is currently married but separated from her husband, because she couldn't forget her first love from before her marriage, who is also the Father of her eldest daughter Mio, and is also the Enshrined Local God of the region (aka., Mio is basically a half-god).
While she had her second daughter with her arranged marriage husband, but because of emotional detachment, she couldn't love him, and so he left her.
Also, Miyako (aka., the 2nd daughter) is more interested in getting her older sister Mio hitched with MC, and doesn't seem to have any romantic feelings towards him (though for reasons she interacts with MC more than her older sister).