The twins will start in the club's development team but Hayden said they hoped to get a a crack at the club's premier team this season.
"We are starting in the development team and they will see how we go then decide whether or not to move us up to play with the big boys," he said. "We have been hitting the gym and going for heaps of runs so we feel in pretty good shape to get started."
Interestingly, the brothers said they were not willing to split up and play for different clubs, when deciding where to play this year, as they played much better together.
"We told Gabriel [from Toro Sports Management] we have to stay together, because we play much better rugby together," Hayden said.
"It is a bit hard to explain, but we can tell what we are both going to do on the field and we are much stronger together."
The twins - who have Samoan heritage - both play in the forward pack with Hayden playing at flanker or lock while Matthew plays at lock.
Hayden said the two would be in South America for eight or nine months and would possibly look at doing a bit of travel after that.
Morales said the twins were a good fit for the club.
"The club had approached me a few years ago and we had been in talks for quite some time [about taking players to Argentina]," he said.
"Based on the boys' profiles and what the club was after I knew it was a good match."
Another John Paul College old boy, Sabi Singh, also headed overseas about a month ago on a similar arrangement to play club rugby in Spain.