I’m not sure why you do not list having children with their sisters as one of your options. As Catholics, I do not believe we have any wiggle room on this issue. Though much of Genesis can be taken symbolically, the Church has been clear, absolutely unwaveringly clear, that humanity began with two people whom we call Adam and Eve. We cannot, as faithful Catholics, just dismiss this teaching because it is uncomfortable. The teaching of original sin hinges on the teaching that all of humanity sprung from two people. The necessity of a Savior for all human kind springs from this very issue. If we believe that Adam and Eve do not represent our first parents, then a lot of things do not make sense. In the words of Pius XII from Humani Generis:
The faithful cannot embrace that opinion that maintains that either after Adam there existed on this earth true men who did not take their origin through natural generation from him as from the first parent of all or that Adam represents a certain number of first parents. Now it is no way apparent how such an opinion can be reconciled with that which the sources of revealed truth and the documents of the teaching authority of the Church propose with regard to original sin, which proceeds from a sin actually committed by an individual Adam and which, through generation, is passed on to all and is in everyone as his own. (HG 37)
I don’t find it burdensome to try to explain how an all Holy God could permit something at one point and then decide it was a bad thing after all. It occurs to me that God decided it was a bad thing, when it became a bad thing. If, genetically speaking, it was not harmful for humans to procreate with close relatives at that point in time then honestly speaking what was the harm? It’s icky? Why is it icky to have kids with your brother or sister? Because at this point in time, we know it is genetically harmful and of course there is a great social taboo. And because we know it is against God’s wishes as laid out in the Mosaic law. But what if there were no genetic problems, and there was no social taboo, and God had not forbid it? What would be the problem then?
I respectfully would like to ask, do you believe Abraham and Sarah are fictional? Or that Isaac is the product of an incestuous marriage? I’m just curious.