Cornelius and Ian followed the route through the paths of the tree of life that Gill, Alan and Manjy had followed before them. Most of the path was the same as that followed by the band of souls on Hoy. They did not, of course, see each other, because the tree of life is entirely subjective. To share Alicia's tree they must have been with her. And they weren't. The astral is a different reality too, but it is objective. Once on the astral they would be able to reach the travellers and the rings.
Cornelius and Ian entered the astral from Binah. A different place where places are not separated by distance. A different time where time is always the same.