In South america on tombstones are last names or maiden names placed first.?

Answer 1

No, in Hispanic countries the double names are required. The wife's maiden name follow her husband's name. It is different than it is in English speaking countries.

Actually this is how it is.

The husband name is his father's followed by his mother's.
The wife and children's name is the husband's followed by the wife's maiden name

until

the daughter gets married. She drops her mother's maiden name, pushes her father's name to the right and then put her husband's name in front of her father's name.