HUNTB-123 - The sister-in-law who can't say no gets taken by my friend, so I decide to join in

My plain sister-in-law is a hidden busty girl who can't say no to anyone. I had a crush on her, but my idiot friend easily gets her to touch her breasts. Coming home to find them having sex, I'm shocked, but since she can't refuse, I decide to take my turn.