[Mrs. Don-o]

Yes, incest would be an unlawful union, and in the Catholic Church would lead to a finding of nullity (annulment).

I will refrain from any judgment concerning Adam and Eve’s children. This would seem to be a one-off exceptional situation where every single human bring on earth is literally your 1st or 2nd degree blood relative.

[Songcraft]

Likewise, while the Ten Commandments had not yet been revealed by Moses, children still obeyed and honored their mother and father, as later explicitly commanded in the Ten commandments (example - Isaac & Abraham).   But Adam and Eve would have been the only two people in the Old Testament who would not have been able to honor their human father and mother, as they didn't have any.