True. However, I can give you benefit of the doubt and assume you are logical and rational.
If you can present no rational argument as to why a sterile adult father and sterile adult daughter should not get married then I assume you would act rational and say it would be ok. If this is not the case and you are not a rational thinker, please forgive me.
Note: We are not talking about what YOU would do with your daughters. We are talking about OTHER people who are doing others no harm.