The twins' group was completely oblivious to the changes to the living chosen ones in the palace. Why would they know anything anyway? They have been stuck in the same region for seven years straight!
The twins spent a very long time in the Dark Region, and that allowed quite a few groups to pass ahead of them before they came out. There were obviously those who didn't even find the Astral Tree, as you had to be at a certain distance to even see it. Those ones simply crossed the region normally.
Since Rifindio already had four marks, that meant only four more mark owners were out there, and none of them ended up coming to the Astral Tree in the years that followed. First of all, if you were a chosen and knew there were more like you, you would expect the other ones to also continue to make their way deeper into the Golden Palace. You would expect to find them easier further down the road.
