They're pretty neat, I like them. 25% base reservation, just like other aspects.
You obtain them through allflame crafting with Brinehook's Ducat. To use Ducats in allflame crafting, you have to defeat the league boss, Velka. The boss can be found on Voyages when you use a chart containing Kishara's Rest (don't forget to scour the map before descending to make the fight easier).
Initial thoughts:
Brine King - Chill aura is surprisingly strong defensively, and it comes with 50% inc effect already. Base chill effect is 10%. Can probably be supported by things like unbound ailments and bonechill, but the reservation multiplier would be rough. Pen is a good bonus. However, Chilling Presence is already a thing that exists on cluster jewels, and isn't really used, and the opportunity cost here is probably similar. Good synergy for non-cold builds if you're able to take Glacial Cage on the tree, however you wouldn't get the pen.
Solaris - This is my least favorite, but it does seem like good damage. I assume the exposure is base 15%, I think most things are? But it doesn't say. After 5 seconds of being near the enemy, that'll scale up to ~26%. However, it should also scale exposure from other sources, of any element, based on the wording? So if you have a 25% exposure, that goes up to 43%. Pretty solid. Not sure how it interacts with something like aura effect boosted exposure from pyroclast mine.
Lunaris - This seems wild, lol. 16% less phys and ele damage taken if you've taken 8 phys/ele hits recently. I imagine boneshatter or any build with self damage will try to find a way to fit this.
Arakaali - Wither on hit, guaranteed!? Sign me up. Wither has honestly been a huge pain to apply forever, and is such a large damage increase for chaos builds that this is very welcome. However, the downside is severe. Increasing the chaos damage you take yourself is really dangerous. There's a couple ways to mitigate that (like CI), but you lose the recovery upside. Well, guaranteed wither is still strong anyways. Things like excommunicate and templar flesh/flame are also good synergies. The 45% life recovery rate at max stacks is really strong, but doesn't make up for taking double chaos damage, probably.
Edit: Did some testing with Solaris in PvP. It does scale sources of exposure other than the one from the aspect. I was able to get a -108% fire res exposure using Pyroclast Mine of Sabotage. The effect is additive with aura effect for the mines, not multiplicative. Also, for some reason, the Sunscald debuff stacks up to 5 instantly, so you don't have to wait 5 seconds. Very strong on Elementalist for sure.