Eu vou preparar o almoço para minha família.

You can leave it out. Portuguese often drops subject pronouns when the verb form already makes the subject clear.

So both of these are natural:

Eu vou preparar o almoço para minha família.
Vou preparar o almoço para minha família.

Including eu can add emphasis, contrast, or just make the sentence a little more explicit.

Vou preparar is a very common future structure in Brazilian Portuguese:

vou = I go / I am going
preparar = to prepare

Together, vou preparar means I’m going to prepare or simply I will prepare.

This structure is:

present tense of ir + infinitive

So it works like this:

eu vou preparar = I am going to prepare
você vai preparar = you are going to prepare
nós vamos preparar = we are going to prepare

You can say prepararei, but in everyday Brazilian Portuguese, vou preparar is much more common.

Compare:

Vou preparar o almoço = very natural in normal speech
Prepararei o almoço = correct, but more formal, literary, or official-sounding

So for spoken Brazilian Portuguese, vou preparar is usually the better choice.

Portuguese uses definite articles more often than English does.

Here, o almoço means the lunch, but in English we often just say lunch. Portuguese normally keeps the article in this kind of sentence.

So:

preparar o almoço = prepare lunch / prepare the lunch

In this context, the article sounds natural because it refers to the meal as a specific thing.

Para means for or to, and here it shows who benefits from the action.

So:

para minha família = for my family

It tells us who the lunch is being prepared for.

Because por and para are not interchangeable.

In this sentence, you want para because it marks the beneficiary: the lunch is for your family.

Por usually has other meanings, such as:

• by
• through
• because of
• per
• sometimes for in a different sense

So por minha família would not mean the same thing. It could sound like because of my family or on behalf of my family, depending on context.

Because the possessive agrees with the noun that follows it.

The noun here is família, which is feminine singular. So the possessive must also be feminine singular:

minha família = my family

Compare:

meu irmão = my brother
minha irmã = my sister
meu almoço = my lunch
minha família = my family

So the form depends on the gender and number of the thing possessed, not on the speaker.

Both are possible in Brazilian Portuguese.

You can say:

para minha família
para a minha família

In Brazilian Portuguese, the article before a possessive is often optional, especially in everyday speech. Usage can vary by region, style, and personal preference.

So the version in your sentence is completely natural and correct.

Preparar is very natural here.

Preparar o almoço means prepare lunch in a broad sense. It can include cooking, arranging, serving, or getting the meal ready.

Cozinhar means to cook, so it focuses more specifically on the act of cooking.

So:

Vou preparar o almoço = I’m going to prepare lunch
Vou cozinhar = I’m going to cook

If you mean the whole meal process, preparar is a great choice.

Yes. In spoken Brazilian Portuguese, pra is extremely common.

So a very natural spoken version is:

Eu vou preparar o almoço pra minha família.

Or even more naturally in conversation:

Vou preparar o almoço pra minha família.

Use para in more careful or formal writing, but pra is everywhere in speech.

A rough pronunciation guide is:

Eu vou preparar o almoço para minha família
≈ ehw voh preh-pah-RAR oo aw-MOH-soh PAH-rah MEE-nyah fa-MEE-lya

A few helpful pronunciation notes:

• eu sounds roughly like ehw
• vou sounds like voh with a slight glide
• almoço has ç, which sounds like s
• minha has nh, a sound similar to Spanish ñ
• família is stressed on mí

The natural spoken rhythm is smooth, and in casual speech some vowels may sound shorter or more relaxed.