Thanks to you both.
We've eventually booked a *A redemption flight so Brasilia - GRU on TAM then GRU - EZE on Turkish.
From reading the above, I'm a bit confused now though! As far as I can tell, we will be able to check in online before heading to Brasilia airport. So (1) can TAM check our luggage all the way through to EZE? (2) if we have checked in online, what do we need to do at GRU?