A násznép a helyszínen van.

Because násznép is a collective noun in Hungarian. It means something like the wedding party, the wedding guests, or the whole wedding group.

Even though it refers to several people, grammatically it behaves as a singular noun, so the verb is singular too:

• A násznép ... van. = The wedding party is ...

This is similar to English expressions like the family is here or the team is ready, where one word refers to a group.

Násznép is a fairly specific cultural word. It refers to the group of people connected with a wedding, especially the guests and participants as a body.

It can often be translated as:

• the wedding party
• the wedding guests
• the wedding procession/group

Depending on context, it may sound a little more traditional or ceremonial than just guests.

It is made up of:

• nász = wedding / marriage-related
• nép = people

So the literal idea is something like wedding people.

Both a words are the Hungarian definite article, meaning the.

So:

• A násznép = the wedding party
• a helyszínen = at the venue / at the location

Hungarian uses the definite article before nouns much like English does, so it is perfectly normal to have it twice in one sentence.

Because helyszínen includes a case ending showing location.

• helyszín = location, venue, scene
• helyszínen = at the location / on the scene / at the venue

The ending here is -n, one form of the superessive case, which often expresses on or sometimes idiomatically at.

So Hungarian often uses a noun + case ending where English uses a preposition:

• a helyszínen = literally something like on the venue/location
• natural English: at the venue, on site, at the scene

That is a very common question, because Hungarian does often omit van in the present tense—but not in all situations.

With noun/adjective predicates, 3rd person present usually has no verb:

• A násznép fáradt. = The wedding party is tired.
• A helyszín szép. = The venue is beautiful.

But with location, Hungarian normally uses van:

• A násznép a helyszínen van. = The wedding party is at the venue.
• Péter otthon van. = Péter is at home.

So here van is necessary because the sentence says where someone is.

All three are possible depending on context, but they have slightly different shades of meaning.

• at the venue → best for a wedding context
• on site → more neutral, practical, event/logistics tone
• at the scene → often used for accidents, crimes, reporters, police, etc.

Since the subject is násznép, the most natural translation is usually:

• The wedding party is at the venue.

But if the broader context is organizational, The wedding party is on site could also work.

Yes, but in a fairly neutral way.

A násznép a helyszínen van. is a normal, straightforward sentence meaning:

• topic: A násznép = the wedding party
• new information: a helyszínen van = is at the venue

Hungarian word order is flexible and often changes emphasis.

For example:

• A násznép a helyszínen van.
  Neutral: The wedding party is at the venue.

• A helyszínen van a násznép.
  More like: The wedding party is at the venue / It’s at the venue that the wedding party is.
  This can sound more marked or context-dependent.

So the original sentence is the most natural neutral order.

A few helpful points:

• Hungarian stress is almost always on the first syllable.
• á is a long vowel, roughly like a longer a sound.
• sz is pronounced like English s
• s by itself is pronounced like English sh
• é is a long ay/eh-type vowel

So roughly:

• násznép → NAAS-nayp
• helyszínen → HELY-see-nen

And the whole sentence is stressed mainly at the start of each word:

• A NÁSZnép a HELYszínen van.

Because helyszín is more specific than a general word like hely.

• hely = place, spot
• helyszín = venue, location, scene

For an event such as a wedding, helyszín is very natural because it refers to the designated event location.

So a helyszínen van sounds more like:

• is at the venue
• is at the location

rather than just is there somewhere.

Yes, you could, but it means something slightly different.

• A násznép a helyszínen van. = The wedding party is at the venue.
• A násznép ott van. = The wedding party is there.

So ott only gives a general there, while a helyszínen names the location more specifically.

If the location is already clear from context, ott van is perfectly natural. If you want to state the actual place, a helyszínen van is better.