The whole point is that there is nothing in the constitution that defines the term. Therefore, it will all be opinion, and they’re not going to make this decision based on one person’s opinion over another’s.
It will be made politically.
There are hundreds of words in the Constitution that are not "defined in the Constitution" because their meaning is a given.
Read the following link...
The term natural born citizen was first codified in the legal reference book "Law of Nations" in 1758, of which was used by John Jay who later became the first Chief Justice of the U.S. Supreme Court. John Jay considered the outstanding legal scholar of his time had the "natural born citizen" clause inserted into the U.S. Constitution via a letter he wrote to George Washington, the leader of the Constitutional Convention..."The Founders required the President to be a "Natural Born Citizen" to help ensure that the ONE person sitting at the top of the Executive branch had unquestionable and unwavering loyalty to the United States of America, first and foremost.
Any Supreme Court uncompromised by expediency and dirty politics would have to decide in favor of the two-parent definition of natural-born citizen.