Thanks everyone!

I contacted Latam, but they still don't know which flight will be moved when. I don't want to wait until April (when they will start moving the flights) to book our flight, so I will have to take the chance. It will be all on one ticket (SCL - AEP - IGR), so Latam will need to take care of it, I guess (that's what they said).

As for Austral, they have 2 different fares, a cheaper one (about 100USD per person) with 15 kg (+8kg for carry-on) and no seat allocation and a more expensive one (about 170USD per person) with the same baggage allowance but on which you can choose your seats. As it will be for 4 people, the more expensive fair is about 300USD more... We don't mind sitting by 2, but I would not want the kids to sit on their own (they are 8 and 10), so I was trying to understand if they usually keep minors with an accompanying adult.

Marambio, you say there is a website where I can buy the tickets and choose my seats regardless of the fare? Are you able to link it here please? I was using Aerolíneas Argentinas (which is giving an error at the moment).

Thanks!