"Jehovah witless (mildly offensive)" joke

The comment yesterday reminded me of my encounter with disciples of Jehovah. The encounter was very entertaining (for me) and very timely. At the time I was doing research on the evolutionary significance of religion and its functional utility. But that is neither here nor there.
Anyway, They came to my door and I immediately invited them in. "I've been waiting for someone like you!", I exclaim and immediately begin to interrogate them on the literalness of the Bible.
They, of course, said that the Bible should be interpreted literally.
They fell right into my trap. My first question was, "Well, Adam and Eve were the first humans on Earth right?"
"Right"
"Therefore, we are all sons and daughters of A & E right?"
"Right"
"Doesn't that mean that the following scenarios are the only possibilities:
Eve had sex with her sons
Adam had sex with his daughters
or their daughters and sons were having sex with each other?
Thank-you but I don't plan to subscribe to any religion that promotes incestuous relationships according to there own doctrine. Good-day.
Needless to say they weren't impressed but maybe they went away and converted to animism or something.