Na vjenčanje dolazi rodbina iz dva grada, pa će stan biti pun gostiju.

Croatian uses na with certain events and occasions, so na vjenčanje means to the wedding.

A useful pattern is:

• ići na vjenčanje = to go to a wedding
• doći na sastanak = to come to a meeting
• pozvati nekoga na ručak = to invite someone to lunch

Here na is followed by the accusative case, because it expresses movement toward an event.

So:

• vjenčanje is nominative/accusative singular
• na vjenčanje = to the wedding

Because rodbina is grammatically a singular collective noun. It refers to a group of relatives, but Croatian treats it as a singular noun.

So the verb is singular:

• Rodbina dolazi. = The relatives / the family are coming.

This is similar to how some English collective nouns can behave, though Croatian is more consistent here.

Compare:

• rodbina dolazi = singular verb
• gosti dolaze = plural verb, because gosti is a regular plural noun

So in your sentence, dolazi is correct because it agrees with rodbina.

Rodbina is in the nominative singular, because it is the subject of dolazi.

The structure is:

• rodbina = subject
• dolazi = verb

So:

• Rodbina dolazi = The relatives are coming

Even though the meaning involves many people, the grammatical form is singular nominative.

The preposition iz always takes the genitive case and usually means from or out of.

So:

• iz grada = from the city
• iz dva grada = from two cities

Here is the breakdown:

• dva = two
• grada = genitive singular form used after dva with many masculine and neuter nouns

This is one of those number patterns Croatian learners need to get used to:

• jedan grad
• dva grada
• tri grada
• četiri grada
• pet gradova

So iz dva grada literally means from two towns/cities.

After the numbers dva, tri, četiri, Croatian usually uses a special form that often looks like the genitive singular for masculine and neuter nouns.

So:

• dva grada = two cities
• tri grada = three cities
• četiri grada = four cities

But from pet onward, you use the genitive plural:

• pet gradova = five cities

So:

• dva grada is correct
• dva gradovi is incorrect
• dva gradova is also incorrect in standard Croatian

Here pa means something like:

• so
• and so
• therefore
• sometimes simply and then

In this sentence, it connects the two ideas in a natural, spoken way:

• relatives are coming from two cities,
• so the apartment will be full of guests.

It is not exactly the same as:

• i = and
• ali = but

So here:

• ..., pa će stan biti pun gostiju. = ..., so the apartment will be full of guests.

It gives a sense of consequence or continuation.

Both are possible.

Croatian future tense often uses:

• ću, ćeš, će, ćemo, ćete, će
  • infinitive

So the neutral basic form would be:

• Stan će biti pun gostiju.

But Croatian allows fairly flexible word order, and in this sentence će stan biti is also natural, especially in connected speech after pa:

• ..., pa će stan biti pun gostiju.

This word order can sound slightly more flowing or stylistically smoother in context.

So both are grammatical:

• Stan će biti pun gostiju.
• Pa će stan biti pun gostiju.

The adjective pun (full) normally requires the genitive case for the thing something is full of.

So:

• pun vode = full of water
• puna energije = full of energy
• pun gostiju = full of guests

Here gostiju is the genitive plural of gosti.

So the phrase means literally:

• full of guests

This is a very common Croatian pattern:

• biti pun + genitive

Stan means apartment/flat, while kuća means house.

So:

• stan = an apartment
• kuća = a house

In your sentence, stan tells us that the people will be in an apartment, not a detached house.

Examples:

• Živim u stanu. = I live in an apartment.
• Živim u kući. = I live in a house.

Yes, but the meaning changes slightly.

• rodbina = relatives / extended family as a group
• rođaci = relatives/cousins, more countable and concrete as individual people

So:

• Rodbina dolazi. = The relatives/family are coming.
• Rođaci dolaze. = The relatives/cousins are coming.

If you use rođaci, the verb must be plural:

• Rođaci dolaze...

If you use rodbina, the verb is singular:

• Rodbina dolazi...

It can be either city or town, depending on context. Croatian grad covers both more broadly than English sometimes does.

So iz dva grada could mean:

• from two cities
• from two towns

If no extra context is given, either translation may be fine. English choice depends on what sounds most natural in the situation.

Yes. Croatian word order is relatively flexible, as long as the case endings make the relationships clear.

For example, these are all possible with slightly different emphasis:

• Na vjenčanje dolazi rodbina iz dva grada, pa će stan biti pun gostiju.
• Rodbina iz dva grada dolazi na vjenčanje, pa će stan biti pun gostiju.
• Pa će stan biti pun gostiju jer na vjenčanje dolazi rodbina iz dva grada.

The original version sounds natural and gives emphasis first to the event:

• To the wedding are coming relatives from two cities,
• so the apartment will be full of guests.

Yes, it is completely natural.

Croatian often uses the present tense for planned or expected events, especially when English might use is coming or even will come.

So:

• Rodbina dolazi na vjenčanje. can mean
• The relatives are coming to the wedding.

This present tense often has a future or scheduled sense, depending on context.

In your sentence, the first clause uses present tense:

• Na vjenčanje dolazi rodbina iz dva grada

and the second clause uses explicit future:

• pa će stan biti pun gostiju

That combination is very normal in Croatian.