We flew our bike into Buenos Aires from Cape Town, versus shipping by sea. But we did experience some hassle at Customs, which was due to new staff not understanding the concept of a carnet de passage.
What finally did the trick was a letter from our auto association in Spanish to whom it may concern explaining the concept. You might find whoever is arranging your carnet could give you a similar letter. Argentina does use carnets, but they are not mandatory.
A Spanish speaker among your group will make things much easier both at customs / borders and generally in South America.