I think it's mentioned somewhere that the Double Helix are located towards the galactic core; I think the Mantu or the Nephilim are supposed to be located out towards the galactic rim. I might have that backwards, though, or maybe they're both located coreward.
Their communication method is obviously supposed to be technobabble, and as technobabble it's not supposed to be understandable, but I think the basic gist of the idea is that it's supposed to be sorta musical, encoded into physical form (chemicals, rather than photons or sound waves like we use).
As for how they don't see history in the same way as humans, I think it's mentioned specifically somewhere that the Double Helix have no sense of history in the sense that one event leads to another (causality). Human beings have the idea that they move through time, but for the Double Helix, time simply exists, and it doesn't make sense to impose any sort of sequence of events on the past.
In science fiction, that sort of capability is often associated with an omniscience about past and future events (the timeline is fixed, it does not change, we simply perceive to be moving through it), but from reading LOAF's blurb, I don't think it's stated anywhere that the Double Helix know anything about the future. More likely, the Double Helix simply have a mentality that doesn't think about things that way; it's not a perfect comparison, but you could think of it like how lower animals don't really have a concept of the past, but only live in the here and now. Since the Double Helix are sentient, they probably know about past events, but just don't think of them as being in the past.