La casa appartiene a mia sorella.

In Italian, appartenere normally takes the preposition a to show who something belongs to.

So the pattern is:

[thing] + appartiene + a + [person]

Examples:

• La casa appartiene a mia sorella.
• Questo libro appartiene a Luca.

This is just how the verb works in Italian.

Because a is required by the verb appartenere.

It does not mean motion here, like to in I go to Rome. Instead, it marks the person something belongs to:

• appartiene a me = belongs to me
• appartiene a lui = belongs to him
• appartiene a mia sorella = belongs to my sister

With singular family members, Italian often omits the article before the possessive.

So you usually say:

• mia sorella
• mio fratello
• mia madre
• mio padre

Not:

• la mia sorella in normal usage

This is a special pattern with close singular family relationships.

But the article usually appears:

• with plurals: le mie sorelle
• with modified family nouns: la mia sorella maggiore
• in some special or regional uses

Italian usually uses the definite article more often than English.

Here la casa simply means the house. Since casa is a singular feminine noun, it takes la.

Article + noun:

• la casa
• la macchina
• la porta

If you removed the article and said just casa, it would usually sound incomplete in this kind of sentence.

Because casa is grammatically feminine in Italian. That is why it takes:

• the article la
• feminine agreement where needed

So:

• la casa
• una casa

Grammatical gender in Italian is a property of the noun itself. It does not imply anything about real-world gender.

No. The infinitive is appartenere.

Appartiene is the third person singular present tense form, used with la casa:

• io appartengo = I belong
• tu appartieni = you belong
• lui/lei appartiene = he/she/it belongs
• noi apparteniamo
• voi appartenete
• loro appartengono

Since la casa is singular, you use appartiene.

Yes. That is also correct and very common.

Both mean essentially the same thing:

• La casa appartiene a mia sorella.
• La casa è di mia sorella.

The version with appartenere can sound a little more formal or explicit, while essere di is often very natural in everyday speech.

That is the normal structure with appartenere:

La casa + appartiene + a mia sorella

Italian word order is often similar to English here. The thing being talked about comes first, then the verb, then the person it belongs to.

You could change word order in special contexts for emphasis, but this sentence is the standard, neutral order.

Usually, in a neutral statement like this, you say mia sorella.

Sorella mia is possible, but it is more expressive, emotional, literary, or emphatic, somewhat like saying my dear sister or stressing the relationship.

So here the normal choice is:

• mia sorella

It is pronounced approximately like:

ap-par-TYE-ne

A more careful breakdown:

• ap as in up but shorter
• par
• tie with a tye sound
• ne

The stress falls on tie: apparTIÈne

If helpful, the infinitive appartenere is stressed differently: apparteNÈre

It can refer to either, depending on context.

Appartenere a can mean:

• legal ownership: the house is owned by my sister
• more general belonging: something is my sister's

With la casa, people will often understand real ownership unless context suggests something looser.

You would normally use an indirect pronoun:

• La casa le appartiene. = The house belongs to her.

Here:

• le = to her

Other forms:

• mi appartiene = belongs to me
• ti appartiene = belongs to you
• gli appartiene = belongs to him
• ci appartiene = belongs to us
• vi appartiene = belongs to you all
• gli appartiene / appartiene loro = belongs to them

In everyday speech, Italians often choose a fuller form if needed for clarity:

• La casa appartiene a lei.

No. It can also mean to belong to in the sense of being part of a group or category.

For example:

• Appartengo a questo gruppo. = I belong to this group.
• Questa parola appartiene al linguaggio tecnico. = This word belongs to technical language.

In your sentence, though, it is about possession or ownership.