Which one is correct?

It's the first. "that" is a pronoun for "guild" which is a thing and so takes the third person.

Anonymous"We're a social guild that helps others" or "We're a social guild that help others"Not sure but I think it's the second one?

AmE: The guild helps others.
BrE: The guild help others.

The same distinction usually applies to all nouns that refer to a group of people, e.g, team, family, committee.

CJ

In British English, we wouldn't say "the guild help others". There's no difference to US English in this regard.

Michael Chambers Teaching EnglishIn British English, we wouldn't say "the guild help others". There's no difference to US English in this regard.

Is the same true of the others I mentioned?

CJ

I thought about it more. We can always use these words as a singular "it" in any situation.

As a formal alternative when talking as "we", you can use the plural forms.

e.g. "The committee are now inviting applications."

There may be more to it than I've said but so far, this feels right.