YOU SAID:

I ain't seen two pretty best friends, always one of them gotta be ugly

INTO JAPANESE

私は2人のかわいい親友を見ていない、常にそのうちの1人が醜くなければならない

BACK INTO ENGLISH

I haven't seen two cute best friends, always one of them must be ugly

INTO JAPANESE

私は2人のかわいい親友を見ていない、常にそれらの1つは醜いに違いない

BACK INTO ENGLISH

I haven't seen two cute best friends, always one of them must be ugly