You do know you are putting forth an extreme case of the strawman fallacy?
The quote from which you are arguing for death is regarding deliberate incestual intercourse. Inappropriate touching is a long way from it, especially when the sisters were not willing participants.
The quote also does not specify death as the punishment, that is another overreach you have put forth to increase the shock value of your emotional argument.
Bad form old chap.
My point is that if you dig, and situate yourself right, you can find moral backing for things that might really not be all that applicable in modern times.