Do you think a Heir of Light would be able to communicate with a different session while being in theirs ? (not like the trolls or Calliope with the kids, just people in a session talking with people from another session) If not, which god tier could do it ? Thank you and I'm sorry if I'm not clear enough.

I don’t quite see the Heir of Light having much to do with communication between Timelines, if anything I feel perhaps a Seer or Mage of Space would be more fitting. To interact with another Session, the most important thing is knowing about them in the first place- Otherwise you may not be able to quite interact with anyone else out there.