I HAVE NOT in fact BUT I WILL NOW. Gather round... I'll try to keep this short though I lost my ramble once alrdy...
8's dream was to teach others about her own culture + uniting octolings and inklings together in harmony, and Splatsville ended up being where that dream led her. She did live in Inkopolis for a while but grew disappointed with the indifference of inklings to anything but themselves, so with help from OtH she rented an apartment on the outskirts of Splatsville. She started working at a shelter near Hammerhead Bridge, where other Octolings much like herself trickled in after leaving the oppressive Octarian society. There she taught Inkling and Octoling languages, though she was still learning the Inkling language herself. 4 started volunteering in the same shelter in their spare time a couple months after. They didn't rly cross paths until 4 started bringin his guitar and playing music for staff and ppl staying at the shelter which caught 8s attention. The song that caught her attention was prolly Calamari Inkantation. They bonded over their shared love for music, at some point 4 invited her to one of his band's gigs (did I mention he's part of my splatband...) aand then they started dating after :3 They didn't know of each other's agent statuses at all till one thing lead to another, 8 introduced 4 to OtH and by extension reintroduced him to Cuttlefish & SS. Lots of angst w the latter but that's a wholeee nother story lol!

HELLOOO ANON I JUST SAW THIS BUT YES. I LOVEEE THAT. And I do think they're naturally submissive, tho it depends what the mask wearer commands of them. They'll bend to whatever the mask wearer's will is, without question
But I do have more specific headcanons if U want to listen... to put it simply I think the helmet members take after the mask wearer and they're all a hivemind, if that makes sense. My hc ab Parallel Canon is is that all the group members are fractions of the mask wearer's soul (being 4) (as a consequence of grayscaling 4 shenanigans). My 4 is submissive so they whole group would prolly be submissive to 8 LOL. They'd all be very eager to please her and/or be used by her.

Yess that is my 8! :^] She just goes by... well, Eight! and Parallel Canon is my ex-4, Zeph, tho more like fragmented versions of them.
Zeph works for Marina as head of Memverse security but due to working with early versions of the simulation, parts of their soul get extracted by Order, making those fragmented versions of them. Being my explanation for why there's a new 4 to fight every time lol.
As of Side Order Eight and Zeph have been dating for a couple yrs but goin thru a rough patch so uhhh some unresolved tension there ig! For the time being Eight went with OtH for their tour and to take some time away from Splatsville. OtH are like her family, particularly she thinks of Marina as her big sister. She'd introduced them both to Zeph a year prior, around the time Marina was starting development of the Memverse. Leading Marina to ask for their help in system security...
Eight was unaware of Zeph's involvement in the Memverse, since they were workin remotely for Marina even before Eight became aware of the project. Soo it was a big shock to see them in such a state!

There's more for me to ramble about but I'll stop there lol... but feel free to ask more specific questions :3