I'm laughing my ass off, reading this thread.
Ok, let's say this was the perfect open world game, with absolute freedom.
Even in such a game, the MC, trying to kill the gang because: "They were (consensually) fucking my family (while I was the only one supposed to fuck them!!!!)" would end
1) either killed by the gang in retaliations and self defense (with them then free to fuck the aforementioned family girls, while the MC is rotting six feet under the ground)
2) or in prison with a life sentence, (with other people fucking the aforementioned family girls, while the MC is fucked by some big guys sharing the cell with him)
So, if you, people, are so scared about NTR, make a favor to the world: imagine this game is such an open world game, imagine one of the two options above as consequences of your choices and then imagine a nice "GAME OVER" screen.