Sina Ana at Liza ang kumanta ng duet.

Sina is the plural personal-name marker. It is used when you are referring to two or more named people together.

• si Ana = Ana
• sina Ana at Liza = Ana and Liza

So because there are two people, Ana and Liza, sina is the correct form.

At means and.

So:

• Ana at Liza = Ana and Liza

It simply joins the two names.

Here, ang is not just marking the verb by itself. It introduces the whole phrase ang kumanta ng duet, which means something like the one(s) who sang a duet.

So the sentence has the pattern:

• Sina Ana at Liza = Ana and Liza
• ang kumanta ng duet = the ones who sang a duet

Together, it means:

• Ana and Liza are the ones who sang a duet.

This pattern is often used for identification or emphasis.

Filipino often allows different word orders depending on what is being emphasized.

This sentence:

• Sina Ana at Liza ang kumanta ng duet.

has an identifying or emphatic feel, like:

• Ana and Liza were the ones who sang a duet.

A more neutral version would be:

• Kumanta ng duet sina Ana at Liza.

That simply means:

• Ana and Liza sang a duet.

So the original sentence puts extra focus on who did the singing.

Yes. That is a very natural sentence.

The difference is mainly emphasis:

• Kumanta ng duet sina Ana at Liza. = neutral statement
• Sina Ana at Liza ang kumanta ng duet. = emphasizes that Ana and Liza were the singers

The second version would sound especially natural if someone asked:

• Sino ang kumanta ng duet?
  Who sang a duet?

Answer:

• Sina Ana at Liza ang kumanta ng duet.

Kumanta comes from the root kanta, which is related to song/sing.

It uses the infix -um-, a very common verb marker in Filipino:

• kanta → kumanta

In this sentence, kumanta means sang.

So:

• kumanta = sang

This is an actor-focus verb form, meaning the doer of the action is the focus.

Because with kumanta, the thing being sung is marked with ng when the singer is the focus.

So in:

• kumanta ng duet

the focus is on the singers, Ana and Liza, not on the duet itself.

If you wanted to make the duet the focus, you could say something like:

• Ang duet ay kinanta nina Ana at Liza.
  The duet was sung by Ana and Liza.

So:

• ng duet = the duet is not the main focus
• ang duet = the duet is the focus/topic

Filipino does not use articles in exactly the same way English does.

In this sentence:

• ng duet

can already mean a duet or the duet, depending on context.

If you want to be more explicit about one/a single duet, you could say:

• ng isang duet

But in many everyday sentences, ng duet is enough.

Filipino verbs do not change form to agree with singular or plural subjects the way English verbs sometimes do.

So:

• Kumanta si Ana. = Ana sang.
• Kumanta sina Ana at Liza. = Ana and Liza sang.

The verb kumanta stays the same. Number is shown by the noun phrase, not by changing the verb.

It is a borrowed word, and that is very normal in Filipino.

Many modern Filipino sentences use loanwords, especially for music, technology, school, and everyday conversation. So duet sounds natural.

You may also encounter spellings or forms like duweto, but duet is common and easily understood.

You may hear si Ana at si Liza in speech, especially when the speaker wants to mention each person individually. But sina Ana at Liza is the standard and most natural grouped form.

So for a learner, the safest choice here is:

• Sina Ana at Liza ang kumanta ng duet.

Use sina when treating the two named people as one plural group.