Norwegian rapper “Jaa9” has made music with another norwegian rapper “OnklP” for a long time.
They has made a lot of singles and albums together as “Jaa9 & OnklP”, but they has also made stuff alone and with other people. The last one “OnklP” is also a member of a band named “OnklP & De Fjerne Slektningene” where “De Fjerne Slektningene” is not a band of its own.
generally, if there’s links that need to be added, like socials or an official homepage, that’s a good reason to have a collaboration artist. less so for stuff like Spotify pages, but might still be a reason.
the fact that Wikipedia calls them an artist is a sign for that too. (actually, this page covers all 4 MusicBrainz artists you linked…)
beyond that, it might just be a matter of feeling…
that said, since 3 of the 4 artists have individual socials and 2 of them have websites (the two groups), I believe these artists are entered correctly~
I generally look at how they present themselves. Simon and Garfunkel usually booked gigs as a pair, and release multiple albums as a pair. And their “band name” therefore is those three words “Simon and Garfunkel” instead of “The Sifunks” or whatever.
If two people act as individuals, and work in different partnerships with different people, I tend to treat them as different people. It mainly depends on how much they release in those partnerships.
But mostly I’ll look at how the artist presents themselves. How do they list their own biographies. How do the fans treat them
There is no hard and fast rule as there are always exceptions and overlaps.