This book occurs 20 years after the end of the ATlantean monarchy, maybe it was restored, it could be even they became rulers of Xebel, after all Mera has a claim to that throne. From the clothes they are wearing its clear that they have some royal robes on. Jess wasn't teasing her, as I mentioned before he referred to her parents as king and queen.
As for Jackson Maybe he lives in the confluence and they visited him, or they went on some mission together, That's why Mera says "we're still in the confluence".
Why FS- Aquaman comes out among the last books of FS you should say, not to mention the non marketing by DC for the book. Why the timeline doesn't match? honestly doesn't make sense. You put Andy on JL now readers who will buy it will find a ten year old girl instead.