i don't think the sister wants threesome lmao she just find it interesting when he sees his brother acting like that cuz hes usually stoic but if she did want threesome i think she would have started getting tu... Rain ᴶᵃʳᶜᵒ
the sister doesnt want an exact threesome she basically wants to be part of it but not getting touched or fucked like holding her brother while he is getting fucked
( ̄へ ̄)