Okaay.
But I think arguing that the Obama marriage was invalid hurts your case, not helps it.
It turns Obama into the child of a single woman, who was indisputably a natural-born citizen.
If the marriage is not valid, the biological father’s relevance to citizenship status of the child becomes significantly less valid.
I don’t think so; just because they were not married does mean he is not the father. And the father was, undoubtedly, a British citizen, not an American.
Unless he was born in Kenya. She didn't meet the criteria, according to the laws in existence at the time, for a single citizen parent to transfer citizenship to her child if he was born outside of the USA.