Having rewatched Genesis of Aquarion episode 16 here is my interpretation.
It is Rena that led Silvia to Apollo in the first place. In the OVA the after effect of the dimensional distortions led to a clue where Apollo was.
In the TV series and OVA universes it is Rena who can read the Book of Genesis.
Like Fudo Rena, doesn't age. Which gives me to the speculation on the whole Body, Heart and Soul thing.
Much like in the OVA in the TV universe Apollonius, Celiane and Scorpius were the pilots of Aquarion. Scorpius did back stab Apollonius. But much like Celiane that split into Silvia and Sirius, Apollonius was split... into three pieces. The Aquarion, Fudo and Rena.
Which is why Fudo and Rena knew more what was going on than the rest of them.