What about Obama’s parents and grandparents? Isn’t it a fact that if both Obama’s mother and father and all 4 of his grandparents were not Native Born Citizens, then he can’t be a Native Born Citizen?
Do you mean Natural Born Citizen? No, NBC goes only back to the parents (plural with an S). Both parents must be citizens. Grandparents aren’t in the picture.
No, not even one's parents need be Natural Born Citizens. In PERKINS V. ELG, 307 U. S. 325 (1939), the Supreme Court agreed with the court below which declared Ms. Elg to be a Natural Born Citizen. Her parents were naturalized citizens, who later renounced that in favor of returning to Swedish citizenship. She was however born in the US, of parents who were then citizens, and so she was herself a Natural Born Citizen.
IOW, the only criteria are "born in the country" "of US Citizen parents", how the parents became citizens does not matter. And there is, according to Vattel's "Law of Nations", an exception to the "in the country" requirement for those "born in the Armies" or in "the house of a diplomat". That is because those military or diplomatic parents remain "subject to the jurisdiction" of the nation and are in it's service.