I just checked, and confirmed that. Ivana was not naturalized until 1988, after the three children were born. We don't know if Barron is eligible until we know when Melania was naturalized.
Who's eligible? Tiffany.
Barron was born in March 20, 2006 the same year Melania was naturalized. So if she was naturalized between Jan 1 to Mar 19 he’s good. But as it stands Tiffany is the only NBC.