There is no terminal 4 at BCN. Do you mean T2 (since it’s Air France)?

There are several exits (A, B and C). The exit depends on the airline, luggage or no, arrival from what country, etc.

If you both arrive from a Schengen country and have no luggage you can easily meet up airside and then go through customs together (any exit you like). There are a lot more bars and restaurants to meet airside.

If not, better to meet landside. There is a big Botero statue (a horse) in terminal 2B landside that I something use as a reference point. (Google for “Botero Barcelona airport”.) But the choice of bars is limited. I think there are only 4 bars/restaurants landside in T2A and T2B, none of them very nice.