Mein Bruder und ich spielen abwechselnd Klavier.

Because Bruder is a masculine singular noun in the nominative case here.

The possessive word mein changes like the article ein:

• mein Bruder = my brother
• meine Schwester = my sister
• mein Kind = my child

So mein is the correct form before a masculine singular noun like Bruder.

Because the subject is Mein Bruder und ich, which means my brother and I. That is a plural subject, equivalent to we.

The verb spielen is the wir/sie plural form of spielen:

• ich spiele
• du spielst
• er/sie/es spielt
• wir spielen
• ihr spielt
• sie/Sie spielen

So Mein Bruder und ich spielen = My brother and I play.

Both can be understood, but Mein Bruder und ich sounds more natural and polite in standard German.

Just as in English, speakers often put themselves after the other person:

• Mein Bruder und ich ... = more natural/polite
• Ich und mein Bruder ... = understandable, but less elegant in standard usage

So this is mainly a matter of style and convention.

Here, abwechselnd is being used as an adverb. It describes how they play the piano: alternately, taking turns.

So in this sentence:

• spielen = play
• abwechselnd = alternately / taking turns
• Klavier = piano

It tells you the manner of the action.

German often places adverbs like abwechselnd before the object or later in the sentence, depending on what is being emphasized.

In Mein Bruder und ich spielen abwechselnd Klavier, the order is very natural:

• subject: Mein Bruder und ich
• verb: spielen
• adverb: abwechselnd
• object: Klavier

You could also hear other word orders in different contexts, but this version is normal and clear.

Because after verbs like spielen, German often uses the instrument without an article when talking about the activity in a general way.

So:

• Klavier spielen = to play piano / to play the piano
• Gitarre spielen = to play guitar
• Fußball spielen = to play soccer

If you say das Klavier, you are more likely talking about a specific piano, the physical object, not just the activity.

Yes, very much so. Klavier spielen is the normal German expression for to play the piano.

English usually needs an article:

• play the piano

German usually does not in this expression:

• Klavier spielen

This is something learners simply need to get used to, because German and English structure these expressions differently.

It is in the accusative case, because it is the direct object of spielen.

However, Klavier is a neuter noun, and with no article here, you do not see a visible case ending. So even though it is accusative, the form Klavier looks the same.

If you added an article, you would see:

• das Klavier in nominative
• das Klavier in accusative

So in this case, nominative and accusative look identical.

Because in German, all nouns are capitalized.

So:

• Bruder
• ich is not capitalized, because it is a pronoun, not a noun
• Klavier

This is a basic spelling rule in German and helps learners identify nouns more easily.

Yes. Since Mein Bruder und ich means we, you could say:

• Wir spielen abwechselnd Klavier.

That means essentially the same thing. The original sentence simply spells out who we are.

No. Abwechselnd specifically suggests taking turns, not doing it simultaneously.

So the idea is:

• first one plays
• then the other plays
• then perhaps the first again

If they were playing at the same time, German would use different wording, such as something meaning together rather than alternately.

Yes. In this kind of sentence, German does not use an article, but English usually does.

So:

• Klavier spielen corresponds to play the piano

Even though German just says Klavier, the natural English translation is usually the piano, not simply piano. This is a difference in idiomatic usage between the two languages.