YOU SAID:
why don't we kill his fathers
INTO JAPANESE
彼の父親を殺したらどうだろう
BACK INTO ENGLISH
What if I killed his father?
INTO JAPANESE
もし彼の父親を殺したらどうなるでしょうか?
BACK INTO ENGLISH
What would happen if I killed his father?
INTO JAPANESE
彼の父親を殺したらどうなるでしょうか?
BACK INTO ENGLISH
What would happen if I killed his father?
That didn't even make that much sense in English.