I don't know what you see but I see this hint which I think pretty much explains all of it:
- The whole expression Vi är fem stycken corresponds to 'There are five of us'.
- stycken means 'ones' but is usually not translated.
Typical Swedish: - Hur många äpplen har du? - Fem stycken.
Typical English: 'How many apples do you have? - Five.'
That structure is used when we say "we are one", but that means we are in agreement.
You can say "we are five", but it's unusual, because numbers are not normally used like that in English, and people will wonder "five what?" or think you are all five years old. By default, numbers as adjectives in English almost always refer to the age of the thing(s).
This confuses English speakers learning other languages, and they'll say things like "jag är tjugo" or "je suis vingt", which make no sense.
both are correct in spoken english https://en.wiktionary.org/wiki/there's#Usage_notes
"There's five..." is really only considered "acceptable" because of laziness in knowing/using the correct grammar ... so, when it's said incorrectly so often people start using it and think it's normal and ok. Use "there's five" if you want.......... but be prepared to sound like you didn't pay attention in 4th grade English class.