Read the Constitution, the part after the first comma in clause 5 of Art II Sec 1 exempts the founders because they knew there could not be any natural born citizens for at least 35 years.
The grandfather clause had nothing to do with James Madison choosing to become a Citizen of the French Republic as well as a U.S. citizen in 1792. And he was “The Father of the Constitution.”
Presidents James Buchanan and Chester Arthur had fathers born in Ireland; Woodrow Wilson’s mother was born in England; Herbert Hoover’s mother was born in Canada, Barack Obama’s father was born in Kenya; and Donald Trump’s mother was born in Scotland.
I agree that Martin Van Buren was the first president to ge a natural born citizen. The seven before him were born as British subjects.