Cantamos un dúo juntos.

In Spanish, subject pronouns are often omitted because the verb ending already shows who is doing the action.

• cantamos = we sing / we sang
• The ending -amos tells you it is we.

So nosotros cantamos is possible, but it usually adds emphasis, contrast, or clarity. In a normal sentence, just cantamos sounds natural.

It can mean either one.

For cantar, cantamos is both:

• present tense: we sing
• preterite: we sang

So without context, the sentence is ambiguous. Context usually makes the time clear.

For example:

• Ahora cantamos un dúo juntos. = Now we sing a duet together.
• Ayer cantamos un dúo juntos. = Yesterday we sang a duet together.

Dúo is a masculine singular noun, so it takes un.

• un dúo = a duet

Here, dúo refers to the musical piece or duet performance. So cantamos un dúo means we sing/sang a duet.

Juntos means together.

In this sentence, it emphasizes that the two people are singing with each other. However, it is somewhat redundant, because a dúo already suggests two people performing together.

So:

• Cantamos un dúo. = already understandable
• Cantamos un dúo juntos. = adds emphasis to together

It is not wrong, but it can sound a little repetitive.

Juntos has to agree with the people involved.

• juntos = masculine plural, or mixed group
• juntas = feminine plural

So if the speakers are:

• two men → juntos
• one man and one woman → juntos
• two women → juntas

If two women were speaking, the sentence would be:

Cantamos un dúo juntas.

It is understandable and grammatically fine, but many native speakers might choose a more idiomatic phrasing.

Common alternatives include:

• Cantamos un dúo.
• Cantamos a dúo.
• Cantamos juntos.

A useful distinction:

• cantar un dúo = to sing a duet
• cantar a dúo = to sing as a duet / in duet form

In Spain, cantamos a dúo can sound especially natural in many contexts.

The accent mark shows the stress and helps indicate the pronunciation.

Dúo is pronounced roughly as:

• DU-o

It has two syllables. The accent mark tells you the stress falls on the first syllable: dú.

Without the accent, the spelling would not correctly show the standard pronunciation.

Yes, Spanish word order is flexible, though some orders sound more natural than others.

For example:

• Cantamos un dúo juntos.
• Cantamos juntos un dúo.
• Juntos cantamos un dúo.

These all work, but they shift the emphasis slightly:

• Cantamos un dúo juntos = neutral, with together added at the end
• Cantamos juntos un dúo = puts together closer to the verb
• Juntos cantamos un dúo = emphasizes together

Yes. Cantar un dúo is a valid literal translation of to sing a duet.

But Spanish also often uses a slightly different structure:

• cantar a dúo

So both ideas exist:

• Cantamos un dúo.
• Cantamos a dúo.

The first focuses more on the duet as a thing; the second focuses more on the way of singing. Both are natural, depending on context.