Also, George P.—being half Mexican
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Correct, his mother was a Mexican national when he was born and he was born with Mexican nationality.
People born with multiple nationalities are naturally not natural born citizens.
Nonsense. Your assertion is not the currently accepted precedent.
George P. Bush was born in Houston, Texas, to an American father, and as such is as Natural Born as you and I doubtlessly are. His situation differs from that of Ted Cruz, who was born in Canada, but is also very likely to be Natural Born.
Inasmuch as George P. Bush is not running for President, I guess that debate isn't too critical right now, but if it was, this information from Wikipedia is informative (emphasis added):
The U.S. Constitution uses but does not define the phrase "natural born Citizen", and various opinions have been offered over time regarding its precise meaning. The consensus of early 21st-century constitutional scholars, together with relevant case law, is that natural-born citizens include, subject to exceptions, those born in the United States. Many scholars have also concluded that those who meet the legal requirements for U.S. citizenship "at the moment of birth", regardless of place of birth, are also natural-born citizens. [2][3] Every president to date was either a citizen at the adoption of the Constitution in 1789 or was born in the United States; of those in the latter group, there have been seven that had at least one parent who was not born on U.S. soil.You could have a Supreme Court composed entirely of nine "strict constructionists"—unanimously selected by a panel composed of Mark Levin, Antonin Scalia, and Clarence Thomas—and they would rule 9-0 that George P. Bush is a Natural Born Citizen, and therefore eligible for the Presidency.
Thus, your interpretation of what constitutes a "Natural Born Citizen" is downright whimsical.
What are you trying to pull?