Hello, I'm from Argentina, specifically from City Bell, La Plata, what a coincidence. Just a detail, if the family is from City Bell, they are not Porteņos, Porteņos are only from CABA (Ciudad Autonoma de Buenos Aires), the capital of Buenos Aires Province.
I don't know anything about regulations for foreign certificates, but as mentioned, would be much easier to hire a safety pilot. Just go to a flight school or an air club and talk with owners and other pilots. There is no need to fly with a CFI, you can also fly with a private pilot seeking hours for the commercial certificate, he is not going to charge anything for that (although I would pay him, so we can stop the "flying for the hour culture". In Argentina a CFI earns 9 USD per hour because they are also building hours). The wet hourly rate without a safety pilot of a Cessna 150 is about 100 usd.