Mm. The in depth answer to this question is hugely plot relative.
So, I'll say this: it has been hinted in previous posts that Aeons are possibly aware of one another, not knowing who/what they are, but gain that sort of instinctual feeling whenever a SOLDIER is near. So, call it a [i]feeling[/i] the Aeons receive in relation to others that translates to the SOLDIER they are fused with. Remember the Aeons were kept alive in minimal states of consciousness through their experimentation and the current state of their beings are leagues different from their true powers and manifest.