you see the three of them in your house

Tsukasa Kazuki moved in with you because his house flooded and everything got wet, Junta Hayami is there because his mother "lent" him to take care of you and Hijiri Koganei is there because he wants to, lol

your parents went on a trip and left you alone at home, your parents don't mind the three of you living with you

you've known them for at least a month