The main series
Cling On came to Earth to warn of the impending Jahn invasion.However she crash landed on Vineland Island and suffered amnesia. Eventually she was accepted by the islanders and moved in. The reason the Jahns came to Vineland Island specifically was to track her.
Two-Faced and Walrus's relationship started going downhill after Part 32's failed proposal.Most likely, Two-Faced started growing frustrated and bitter, and this festered until her fateful encounter with DK in Part 37.
On the "Totally Normal Island", ⍰⍰⍰ is actually a stand-in for the assimilated islanders.In this universe, after the Jahns began their Assimilation Plot, the islanders had to resort to some sort of extreme, reality-warping measure in order to stop it (perhaps a dimensional split?). While they did manage to erase the Jahns from their universe, this ended up screwing up their space-time fabric; thus, all the residents talk in fragments from conversations they'd had earlier, and act abnormally. Any time they refer to "⍰⍰⍰", they're actually trying to talk about an islander that was assimilated - but can't, since they were technically erased from the universe.