In theory 50% of all regional flights , except those to and from Uruguay ,will be moved to Ezeiza on 9th April.
What 50% ? no one is quite sure yet.....
There is a possibility that this date will be moved back - i would imagine that Latam will reaccommodate you if the schedule change means you are unable to do the transfer.
Austral is a subsidiary of Aerolineas Argentinas - so service levels will be fine . Planes will be quite new . Austral operates 737s and EMB 190s/
15 kilos is the normal baggage allowance on domestic flights with Aerolineas / Austral
Normally you can book seats together when you book on theuir webs ite