need advice for team games

me and my mate (in 2v2s, mostly arab) struggle with strategies for midgame. i understand usually earlygame works just like in 1v1, scouts/m@a/archers etc. But: how to go on from there? usually at some point the opponents will unite their armies and double team one of us who then loses his army and dies. the second player can never do enough eco damage to his unprotected opponent to even things out. is double attack on one player always the best option? how to decide where/which one to attack first? i’m ~1470 voobly. thx