לא רק אני אהיה בבית בערב, אלא גם הילדים יהיו שם, ולכן נכין ארוחה גדולה.

Yes. לא רק ... אלא גם ... is the standard Hebrew pattern for not only ... but also ....

In this sentence:

• לא רק אני אהיה בבית בערב = not only I will be at home in the evening
• אלא גם הילדים יהיו שם = but the children will also be there

It is basically a set expression, so learners should get used to recognizing it as a unit.

Correct: אהיה already tells you the subject is I. Hebrew verbs often contain the subject information inside the verb itself.

So technically, Hebrew could sometimes omit אני. But here אני is useful because it creates contrast:

• לא רק אני ... אלא גם הילדים ...
• not only I ... but also the children ...

So the pronoun is there for emphasis and clarity.

Yes. Both are future forms of להיות = to be.

• אהיה = I will be
• יהיו = they will be

Hebrew works differently from English here:

• In the present, Hebrew usually does not use a word for am/is/are.
  
  • אני בבית = I am at home
• In the future and past, Hebrew does use forms of להיות.
  
  • אני אהיה בבית = I will be at home

So in this sentence, אהיה and יהיו are necessary because the sentence is in the future.

Because הילדים = the children is plural, and the verb has to match it.

• הילד יהיה = the boy / child will be
• הילדים יהיו = the children will be

יהיו is the future plural form, used here for a masculine plural or a mixed-gender group. Since ילדים is grammatically masculine plural, יהיו is the correct form.

בבית means at home or in the house, depending on context.

It is made from:

• ב־ = in / at
• בית = house / home

In this sentence, אהיה בבית בערב most naturally means I’ll be at home in the evening.

A useful thing to know: in normal unpointed Hebrew writing, forms with and without the article can look the same, so context helps you understand whether it means in a house, in the house, or at home.

בערב means in the evening or sometimes this evening / tonight, depending on context.

It is built from:

• ב־ = in
• ערב = evening

So literally it is in the evening.

This is very common in Hebrew time expressions:

• בבוקר = in the morning
• בצהריים = in the afternoon / at noon
• בערב = in the evening
• בלילה = at night

Because גם usually comes right before the word or phrase it emphasizes.

So:

• גם הילדים יהיו שם = the children too will be there / the children will also be there

Placing גם before הילדים clearly marks the children as the added element in the not only ... but also ... structure.

Other word orders are possible in Hebrew, but גם הילדים is the most straightforward choice here.

Here, שם means there.

So:

• הילדים יהיו שם = the children will be there

A good thing to remember is that שם can also mean name in unpointed Hebrew writing. The spelling is the same, and context tells you which meaning is intended.

Here it clearly means there, not name.

ולכן means and therefore, so, or and so.

It is made of:

• ו־ = and
• לכן = therefore / so

So the sentence says that because not only the speaker but also the children will be there, therefore they will prepare a big meal.

This kind of logical connector is very common in written and spoken Hebrew.

נכין means we will prepare.

It is a future-tense verb, and the we is built into the form itself, so Hebrew does not need to add אנחנו unless the speaker wants emphasis.

So:

• נכין ארוחה גדולה = we will prepare a big meal

The subject is understood from the context: the speaker and the children.

Because Hebrew adjectives must agree with the noun in gender and number.

• ארוחה = meal, feminine singular
• גדולה = big, feminine singular

So ארוחה גדולה means a big meal.

Compare:

• ספר גדול = a big book
• ארוחה גדולה = a big meal

If it were the big meal, Hebrew would usually say:

• הארוחה הגדולה

with ה־ on both the noun and the adjective.

Yes, that is grammatically possible, because אהיה already means I will be.

But לא רק אני ... אלא גם הילדים ... sounds more natural here because the sentence is contrasting two subjects:

• not only I
• but also the children

So including אני makes the contrast clearer and more natural.

Hebrew is somewhat more flexible than English, but the word order here is very natural and helps show the structure clearly.

The sentence is organized like this:

1. לא רק
   • first idea
2. אלא גם
   • second idea
3. ולכן
   • result

That gives the sentence a very clear logic:

• not only X
• but also Y
• therefore Z

So even though Hebrew can sometimes move parts around, this order is a good model to learn from.