I'm with those who believe John 8:41 a statement of those Jews that they are true children of God, as this is the clear context of the discussion, the question their Father God, or some other father, like Satan, they were actually behaving as, the Lord Jesus questioning who the father is of those who claim God, yet don't recognize God standing in front of them.
This aside, why are you so very much obsessing over something you can never prove? I can admit it could possibly be true the statement about fornication could have had a snide remark component about Christ's birth, this not impossible, but something nobody could ever prove. So, isn't anything beyond stating your take on that scripture, trying to, as if, insist others enjoin your view a bit like beating a dead horse? If you've stated a case that can't actually be proven, where the differing view is just as valid, doesn't it come down to simply useless disputing after awhile?
Philippians 2:14 Do all things without murmurings and disputings.