It is a tad bit confusing.
But I may be wrong though. I forgot which of the two wont be in the Avengers 2 (Hank or Ant) We might not know. Hank Pym could be in the Avengers 2 but not Ant-Man (phase 3). And throw in Quick Silver and Scarlett Witch who were announced to be in it AND MAYBE if Ultron creates Vision. Things might either get confusing or awesome.
And don't forget. Thanos has other problems up his bum somewhere in the Galaxy. I think Marvel even said that Thanos is puppeting the villains in Guardians.
But I'm confident that the Avengers 3 will most likely involve Guardians of the Galaxy AND Thanos.