"The Sanctuary Duet" review
The Sanctuary Duet takes place at the same time as the Lighthouse Duet but should be read after Lighthouse. However, if you avoided the other duology because you didn’t want to read something quite so dark, but you still want to read something set in Navronne, it is possible to read Sanctuary Duet on its own; you just might be a bit more confused about the worldbuilding than you otherwise would be, because some things are explained less directly than they might otherwise be, assuming the reader already understands what’s going on from having read Lighthouse.