Artist angeltights is actually a group

According to Angeltights's Twitter, they are a collaboration of three artists: SteelyBird, SunFlowerART, and another artist called Kiyomi. I found this out when copying tags from post #10181514 (tagged with Angeltights) to post #10682298 (tagged with SteelyBird), a pixel-perfect duplicate of the former.

Is Angeltights a valid artist tag, or should it just be a group name instead? I know we usually don't make group names arttags, but I can also see how it may be useful if it's unclear which artist made a specific piece of work. Should the posts have both Angeltights and the specific artist, or just the artist?

IMO, it's fine to have arttags for groups because like you said, it can be difficult to tell which artist made which work.
Make a wiki for the arttag and list the artists who are group members. If the member artists have an arttag, then add the group name to their artist entries.
example group arttag: orange_maru

I found some new information from their Patreon. Kiyomi is Angeltights, so I don't know if we can still treat it like a group. What would be the best thing to do in this situation?

I don't think that patreon is run exclusively by kiyomi.
Kiyomi arttag is kiyomi draws. They retweeted angeltights and post similar content.

The pinned tweet by angeltights is a making-of that all 3 artists worked on. This could be either the usual workflow or the process for just this one.
asset #42452254
I think it's a group account where all 3 artists contribute. Most of the account aboutmes use plural pronouns.

I didn't say it was exclusively run by her. The description says "Hello! My name is Kiyomi (Angeltights) Here are 3 artists drawing big soft mommies for you!" It's clear from the description that the Patreon is a collaborative effort, but the wording makes it hard to tell whether Kiyomi is saying "I'm Angeltights" or "I'm part of Angeltights."

In any case, this makes it seem like anything from those accounts should have all three artist tags.

Blank_User said in forum #415514:

In any case, this makes it seem like anything from those accounts should have all three artist tags.

I disagree. I think we should just use the group artist tag for posts from angeltights. The other 3 arttags can be treated the same as before. Unless its explicitly stated who did what, it's ambiguous.