A família cujas netas moram longe vai visitar a avó em dezembro.

Cujas means whose.

So A família cujas netas moram longe means The family whose granddaughters live far away.

It shows a relationship of possession or belonging:

• the family
• its granddaughters

In Portuguese, cujo / cuja / cujos / cujas is a relative pronoun used to connect two nouns like whose does in English.

Because cujas must agree with the noun that comes after it, not with the noun before it.

Here is the pattern:

• cujo
  • masculine singular noun
• cuja
  • feminine singular noun
• cujos
  • masculine plural noun
• cujas
  • feminine plural noun

In the sentence, the next noun is netas, which is:

• feminine
• plural

So the correct form is cujas.

This is a very common question.

Even though família is feminine singular, cujas does not agree with família. It agrees with netas, the noun that follows it.

So:

• a família = the thing being described
• cujas netas = whose granddaughters

Think of it as:

• the family
• whose granddaughters

The word whose in English does not change form, but in Portuguese cujo changes to match the possessed thing:

• cuja filha = whose daughter
• cujos filhos = whose sons
• cujas netas = whose granddaughters

Because that structure is not considered correct standard Portuguese.

Portuguese normally does not use que + possessive there the way English learners might expect.

So this is not the standard form:

• a família que suas netas moram longe

The standard form is:

• a família cujas netas moram longe

In everyday speech, many Brazilians avoid cujo because it sounds a bit formal. They may rephrase the sentence instead, for example:

• A família, que tem netas que moram longe, vai visitar a avó em dezembro.
• A família das netas que moram longe vai visitar a avó em dezembro.
  (This changes the meaning slightly depending on context, so it is not always the best substitute.)

So cujo is grammatically elegant and correct, but somewhat more common in writing and formal speech than in casual conversation.

Yes, generally it sounds more formal or literary than many other structures.

Brazilians understand it perfectly, and it is absolutely correct, but in casual spoken Portuguese people often prefer simpler alternatives.

For example, instead of:

• A família cujas netas moram longe...

Someone might say:

• A família que tem netas morando longe...
• A família, cujas netas moram longe...
  (still formal)
• A família das netas que moram longe...
  (possible in some contexts, but not always identical)

So as a learner:

• you should definitely recognize and understand cujo
• it is useful to learn how it works
• but you should know it may sound more formal than the most conversational option

Because the grammatical subject is A família, and família is a singular noun.

So the verb must also be singular:

• A família vai visitar...

This is similar to English in some cases:

• The family is going to visit...

Even though a family contains multiple people, the noun itself is grammatically singular.

If the subject were plural, the verb would change:

• As famílias vão visitar a avó em dezembro.

Vai visitar is a very common Portuguese future construction:

• ir + infinitive

Here:

• vai = present tense of ir
• visitar = infinitive

So vai visitar means is going to visit / will visit.

This structure is extremely common in Brazilian Portuguese and often sounds more natural in conversation than the simple future.

Examples:

• Ela vai viajar amanhã. = She is going to travel tomorrow.
• Nós vamos sair cedo. = We are going to leave early.

So in your sentence:

• A família vai visitar a avó em dezembro.

means the family is going to visit the grandmother in December.

Because visitar is a direct transitive verb in Portuguese. It takes a direct object without a preposition.

So:

• visitar alguém
• visitar um amigo
• visitar a avó

This is different from verbs that require a preposition, such as:

• gostar de
• precisar de
• ir a / para

So:

• vai visitar a avó = is going to visit the grandmother

The a here is just the feminine singular definite article the, not a preposition.

Portuguese often uses definite articles more than English does.

So where English might say:

• visit grandmother or
• visit her grandmother

Portuguese often says:

• visitar a avó

The article a helps make the noun sound natural and specific.

In this sentence, a avó most naturally means the grandmother or their grandmother, depending on context.

Portuguese frequently uses the article even when English would not:

• Ela foi à escola.
• O João chegou cedo.
• A mãe está em casa.

So a avó is very natural here.

Moram longe means live far away.

Breakdown:

• moram = they live
• longe = far / far away

So:

• as netas moram longe = the granddaughters live far away

Longe is an adverb, so it does not change form.

You can also hear:

• morar longe de alguém / de algum lugar = to live far from someone / somewhere

For example:

• Eles moram longe da cidade. = They live far from the city.

In your sentence, longe appears without naming what they are far from, which is perfectly normal.

Because months are normally used with em in Portuguese.

So:

• em dezembro = in December
• em janeiro = in January
• em agosto = in August

You would not normally say no dezembro for this meaning.

Examples:

• Eu viajo em julho.
• Ela nasceu em março.

So in the sentence:

• vai visitar a avó em dezembro means
• is going to visit the grandmother in December

It describes a família.

The main noun is:

• A família

Then the relative clause adds information about that family:

• cujas netas moram longe

So the full subject is:

• A família cujas netas moram longe

Then the rest is the predicate:

• vai visitar a avó em dezembro

A good way to see the structure is:

• A família = subject head noun
• cujas netas moram longe = relative clause describing the family
• vai visitar a avó em dezembro = what the family is going to do

Yes, and in practice those are probably the same person in this sentence.

The sentence itself does not spell out the relationship in a more detailed way, but the most natural reading is:

• there is a family
• that family has granddaughters
• the family is going to visit the grandmother

Usually the listener understands from context whose grandmother this is. Portuguese often leaves that kind of relationship implicit when it is obvious enough.

If you wanted to make it more explicit, you could say:

• A família cujas netas moram longe vai visitar sua avó em dezembro.
• A família cujas netas moram longe vai visitar a própria avó em dezembro.

But the original sentence is already natural.

The original sentence is correct, but cujas can sound a bit formal.

A more conversational rewording might be:

• A família, que tem netas que moram longe, vai visitar a avó em dezembro.

Or:

• A família com netas que moram longe vai visitar a avó em dezembro.

These are not always perfectly identical in nuance, but they are closer to everyday speech.

So the original sentence is great for learning grammar, especially cujo, while a Brazilian in casual conversation might choose a simpler structure.