If you're trying to bring up the Nauceans, the alien race that seeded Sagan 4 with life and study the planet's lifeforms, you should know the Nauceans are almost never mentioned "canonically". Only 5 Sagan 4 species pages and one meta page directly mention them, although they are implied in the official description of the religion of the Tripodician, and the fact real-life organisms are occasionally referred to as "Terran" (Terran penguin, Terran axolotl, etc.) rather than solely their plain names.
When the Nauceans are canonically mentioned, individuals are not characterized by name. I recommend you ask Hydromancerx about this, but the easiest solution is just to skip including the reasoning for the names.
The picture of Hrethr and Hrothr is surely not to scale. If the islands were close together, the "camera" would be relatively close, and it could detect subtler details, like cliffs, hills, and boulders. They would look so smooth and vaguely-shaped only from a distance, but that would surely make them seem farther apart. Try looking at similar photographs and portraying distance. Alternatively, you can just make a note it's a diagram and not to scale. The island of Santorini is the most straightforward reference for what caldera island(s) can look like.
It appears Hrethr is open to the ocean from the ocean side. That doesn't seem to be the case from the map-derived picture, unless the narrowest point facing the ocean is a low-lying channel that is tidally flooded. If so, that should be specified.
Specifiying the height of each (at least height above sea level) would help in determining what sort of organisms could live there. They're probably fairly low-lying, though. The walls of the calderas seem fairly steep. If they're actually not that steep, it wouldn't require particular specializations to climb them.
If Hrothr's lake is enclosed from the sea, it could be an interesting freshwater feature. Darwin Temperate Desert has no major (e.g., like the Amazon, Nile and Mississippi rivers, and no "great lakes" (e.g., like those of the U.S. or Africa), and it's sandy so the water drains fast. If Hrothr has a freshwater lake, it could be ecologically important for flying organisms, or even aquatic animals that can still move on land and get thirsty if they drink only seawater. (e.g., like sea snakes)
I noticed I've had to give you a lot of guidance with your Moleroot submission, to the point it's more of a collaborative submission. While I'm okay with helping you edit and refine your concepts, if the wording and concept is largely mine, it would exceed the boundaries of what I would accept for a single-person submission. If you have a really bare-bones work-in-progress submission with various problems that you require multiple reminders to fix, it's best to put it on the dedicated work-in-progress thread first, rather than put it on the forum to occupy a submission slot.
Please look at previous landmark submissions to get an idea of what they're like: the naming conventions (e.g., Hrethr & Hrothr Calderas/Hrethr & Hrothr Islands instead), and ecological implications, and interesting geological features. I strongly urge you to pay close attention to the formatting of the template of submissions, too, with a picture on top. I would actually only recommend landmarks to very experienced members, or those with a particular knowledge of geology and/or geographical oddities.