1. George Romney's parents were American, so just because he was born in Mexico, he was still a naturally born American citizen.
2. Even if George wasn't a naturally born American, Mitt Romney was born in the United States, and is thus a naturally born American.
3. Obama had a Kenyan father and American mother. Since he was born in the United States, he's naturally born American. Had he been born in Kenya, he would not have been naturally born because his father was Kenyan but his mother was American who was not yet 18, so she couldn't confer her citizenship to him. Had Obama's mother been 18 when Obama was born, there would have been no birth certificate issue because it would have been moot.
George Romney’s parents owned land, a very large ranch, in Mexico. To own land in Mexico one must be a citizen of Mexico. George was born to parents who where Mexican citizens “NOT” US citizens. That makes George a Mexican citizen. If there are no naturalization papers on George or the papers are dated after Mitt’s birth then Mitt Romney is not eligible for the office of president.