Wenn meine Tochter krank ist, kuscheln wir zusammen auf dem Sofa und hören leise Musik.

Because wenn introduces a subordinate clause in German. In subordinate clauses, the conjugated verb usually goes to the end.

So:

• Meine Tochter ist krank. = main clause
• Wenn meine Tochter krank ist, ... = subordinate clause

This is one of the most important word-order rules in German.

Because the sentence starts with a subordinate wenn clause. After that clause, the main clause begins, and in a German main clause the finite verb must be in second position.

So the structure is:

• Wenn meine Tochter krank ist, = subordinate clause
• kuscheln wir zusammen ... = main clause

This is why German uses:

• Wenn meine Tochter krank ist, kuscheln wir ...

and not:

• Wenn meine Tochter krank ist, wir kuscheln ...

This is often called inversion.

Yes. In German, a subordinate clause introduced by wenn is normally separated from the main clause by a comma.

So this comma is not optional:

• Wenn meine Tochter krank ist, kuscheln wir ...

German punctuation is stricter than English here.

Here wenn means when or whenever.

It can often suggest a repeated or general situation:

• Wenn meine Tochter krank ist, ...
  = When/Whenever my daughter is sick, ...

In many everyday sentences, English speakers can think of wenn as when for present/future situations and whenever for repeated situations.

A useful contrast:

• wenn = if / when
• als = when, for a single event in the past

Because meine Tochter is the subject of the subordinate clause, so it is in the nominative case.

In:

• meine Tochter krank ist

the daughter is the one who is sick, so she is the subject.

You would use meiner Tochter in a different structure, for example in the dative:

• Ich helfe meiner Tochter. = I help my daughter.

Kuscheln means something like to cuddle, snuggle, or cosy up.

In this sentence, it is not reflexive. German can simply say:

• Wir kuscheln. = We cuddle / snuggle.

You can also add words like:

• zusammen = together
• mit meiner Tochter = with my daughter

So kuscheln here works perfectly well without sich.

Zusammen means together.

It emphasizes that we cuddle together:

• kuscheln wir zusammen

In many cases, kuscheln already suggests togetherness, so zusammen adds emphasis or makes the image more natural.

You could compare:

• Wir kuscheln. = We cuddle.
• Wir kuscheln zusammen. = We cuddle together.

Because this sentence describes a location, not movement toward a destination.

German prepositions like auf can take:

• dative for location: where?
• accusative for direction/movement: where to?

Here:

• auf dem Sofa = on the sofa / on the couch
  This tells us where the cuddling happens.

If there were movement onto the sofa, you would say:

• Wir setzen uns auf das Sofa. = We sit down onto the sofa.

So:

• auf dem Sofa = location
• auf das Sofa = direction

Because both verbs share the same subject, wir.

German often links two verbs with und without repeating the subject:

• kuscheln wir zusammen auf dem Sofa und hören leise Musik

This means:

• we cuddle together on the sofa and listen to soft music

You could repeat the subject, but it is usually unnecessary:

• ..., kuscheln wir zusammen auf dem Sofa und wir hören leise Musik.

That sounds heavier and less natural here.

Here leise means quiet, soft, or low-volume.

In leise Musik, it is an adjective describing Musik:

• leise Musik = soft/quiet music

So the sentence means that they listen to music that is gentle or not loud.

Because it is an adjective placed before the noun Musik, and in this sentence Musik has no article.

With no article, German adjectives take what is called a strong ending. Since Musik is:

• feminine
• singular
• accusative

the adjective ending is -e:

• leise Musik

Other examples:

• kalter Kaffee
• gute Suppe
• frisches Brot

Not in this sentence.

Here it directly describes the noun Musik, so it is an adjective:

• leise Musik = quiet music

If it were an adverb, it would describe the verb instead:

• Wir hören leise. = We listen quietly.

That is grammatically possible, but it means something different.

Because in the subordinate clause, the conjugated verb ist goes to the end, and krank is a predicate adjective that stays before it.

Compare:

• Meine Tochter ist krank. = main clause
• wenn meine Tochter krank ist = subordinate clause

So the word order changes because of the subordinate clause, not because krank itself is special.

Yes. In natural German, Wenn meine Tochter krank ist, ... often suggests a general pattern:

• Whenever my daughter is sick, we cuddle together on the sofa and listen to soft music.

It can also fit a specific current situation depending on context, but many learners should understand it as a repeated or typical action unless the context says otherwise.