Learn Hardcore German: Wir sitzen zu zweit auf dem Sofa.

Wir sitzen beide auf dem Sofa.
= “We are both sitting on the sofa.”
Focus: both members of “we” are sitting there (as opposed to only one).
Wir sitzen zu zweit auf dem Sofa.
= “We are sitting on the sofa as a twosome / just the two of us.”
Focus: the group size: there are exactly two people, together as a pair.

Wir beide points to the people themselves (“the two of us”),
zu zweit describes how you are doing something—your group size while doing the action.

In many contexts, they can be interchangeable, but zu zweit makes the “in a group of two” idea more prominent.

Is zu zweit an adjective? Why doesn’t it change its ending?

Zu zweit is used adverbially; it functions like an adverbial phrase (“in a group of two”), not like a normal adjective in front of a noun.

Because of that:

It doesn’t get adjective endings.
It doesn’t change for gender, case, or number.

Examples:

Wir sind zu zweit. – We are two (as a pair).
Sie gehen zu zweit ins Kino. – They go to the cinema as a pair.
Die Kinder arbeiten zu zweit. – The children work in pairs.

In all these sentences, zu zweit stays the same.

Why is it auf dem Sofa with dative, and not accusative?

The preposition auf can take either dative or accusative, depending on the meaning:

Dative: location, no movement to a new place
→ Wo? (Where?)
Accusative: direction, movement to a place
→ Wohin? (Where to?)

In Wir sitzen zu zweit auf dem Sofa:

The question is Wo sitzen wir? – On the sofa.
There is no movement to the sofa, just a location.
So auf takes the dative: auf dem Sofa (not aufs Sofa).

If you described moving to the sofa, you’d use accusative:

Wir setzen uns zu zweit aufs Sofa.
(We sit ourselves down, the two of us, onto the sofa.)

Why is it dem Sofa and not something else? What gender is Sofa?

Sofa in German is neuter: das Sofa in the nominative.

In the dative singular:

Masculine: dem Mann
Neuter: dem Sofa
Feminine: der Frau

So:

Nominative: das Sofa
Dative: dem Sofa

That’s why the phrase is auf dem Sofa.

With an indefinite article:

Nominative: auf einem Sofa
Dative: auf einem Sofa (same form for dative neuter).

Could I say Wir sitzen aufs Sofa instead?

No, not with sitzen.

Sitzen describes a state: “to be sitting.” That goes with a location → dative.
→ Wir sitzen auf dem Sofa. – We are sitting on the sofa.
Sich setzen describes a movement into a sitting position, “to sit down.” That goes with direction → accusative.
→ Wir setzen uns aufs Sofa. – We sit down on(to) the sofa.

So:

Wir sitzen auf dem Sofa. (state, dative)
Wir setzen uns aufs Sofa. (movement, accusative)

Wir sitzen aufs Sofa is incorrect because it mixes a state-verb with a direction case.

Why does German say sitzen instead of something like “are sitting”? Is this a progressive form?

German usually does not use a separate progressive tense like English. The simple present covers both:

Wir sitzen auf dem Sofa.
can mean:
- “We sit on the sofa.” (general / habitual)
- “We are sitting on the sofa.” (right now)

Context tells you which is meant.

So wir sitzen is just present tense of sitzen, and it includes the meaning of English “are sitting” when used in the right context. There is no special grammar form here—just normal present tense.

Can I change the word order and say Wir sitzen auf dem Sofa zu zweit?

Yes, that’s grammatically correct.

Possible versions:

Wir sitzen zu zweit auf dem Sofa.
Wir sitzen auf dem Sofa zu zweit.

Both mean the same. The most common and natural sounding here is probably the original: Wir sitzen zu zweit auf dem Sofa.

General rule: adverbial phrases like zu zweit are relatively flexible. German tends to put “more central” information closer to the verb, but you can move things around for emphasis or rhythm.

Could I also say Wir zwei sitzen auf dem Sofa? How is that different from Wir sitzen zu zweit auf dem Sofa?

Yes, Wir zwei sitzen auf dem Sofa is correct and natural.

Wir zwei sitzen auf dem Sofa.
Emphasis on wir zwei = “we two (and not others).” It highlights who the two people are.
Wir sitzen zu zweit auf dem Sofa.
Emphasis on the group size and togetherness while doing the action.

In many contexts these will feel very similar, but:

Wir zwei often contrasts with someone else: “we two (as opposed to them).”
Zu zweit is more about doing something as a pair, sometimes with a nuance of privacy or intimacy.

Are there similar expressions to zu zweit for other numbers?

Yes, German uses the same pattern for other small group sizes:

zu zweit – as a pair, two together
zu dritt – in a group of three
zu viert – in a group of four
zu fünft – in a group of five, etc.

Examples:

Wir gehen zu dritt ins Kino. – Three of us are going to the cinema.
Sie wohnen zu viert in einer Wohnung. – Four of them live together in one apartment.
Im Auto sitzen sie zu fünft. – There are five of them in the car.

The pattern is very productive and common in everyday speech.

Is Sofa the same as Couch in German, or is there a difference?

In modern German, Sofa and Couch are near-synonyms, and both are widely understood.

Sofa is slightly more neutral and maybe a bit more “standard”.
Couch sounds a bit more informal or colloquial to some speakers, but it’s very common.

You can usually replace:

Wir sitzen zu zweit auf dem Sofa.
with
Wir sitzen zu zweit auf der Couch.

The preposition and case stay the same; only the gender changes:

das Sofa → auf dem Sofa (neuter)
die Couch → auf der Couch (feminine)

Why is it zu zweit and not zu zwei or zu zweien?

Historically, forms like zu zweien (dative plural) exist and are still possible in more formal or older style German, but in everyday language zu zweit has become the fixed, idiomatic form.

Compare:

Everyday, modern:
- Wir sind zu zweit.
- Sie arbeiten zu zweit.
More formal / old-fashioned:
- Wir sind zu zweien. (you might see this in literature, but it sounds marked today)

Zu zweit is treated as a set adverbial expression, so you normally don’t change it. You should avoid zu zwei in this meaning; it sounds wrong to native speakers.