Нам предстоит трудный разговор.

Because this sentence uses a pattern where the person affected is put in the dative case, not the nominative.

• нам = to us / for us
• мы = we

The verb предстоять often works like to be ahead of someone, to await someone, or to be in store for someone. So the structure is closer to:

• Нам предстоит трудный разговор.
• A difficult conversation lies ahead for us.

So нам is not the subject in the normal English sense. It marks the people who are about to face the conversation.

Предстоит comes from предстоять. In this kind of sentence, it means something like:

• to lie ahead
• to be forthcoming
• to await someone
• to be in store for someone

So Нам предстоит трудный разговор means something like:

• We have a difficult conversation ahead of us
• A difficult conversation awaits us

This verb is common when talking about something that is going to happen and is often serious, important, or unavoidable.

Because разговор is the grammatical subject of the sentence.

In Russian, the thing that predstоит—the thing that lies ahead—is usually in the nominative:

• Нам предстоит разговор. = A conversation lies ahead for us.
• Мне предстоит экзамен. = An exam awaits me.

So:

• нам = dative, the experiencer
• разговор = nominative, the thing that is ahead
• трудный agrees with разговор

Because разговор is the subject, so it stays in the nominative singular. The adjective has to match it:

• разговор = masculine, singular, nominative
• трудный = masculine, singular, nominative

So:

• трудный разговор = a difficult conversation

If the noun were in another case, the adjective would change too, but here nominative is correct.

Formally, предстоит is a present-tense form of an imperfective verb. But in meaning, it often refers to the future, because the whole idea is that something is still ahead.

So although it looks present, the sentence means:

• A difficult conversation is ahead of us
• We are going to have a difficult conversation

This is normal for предстоять. Its meaning naturally points forward in time.

Yes. Very often, предстоять is used with an infinitive to mean to have to do something or to be about to face doing something.

For example:

• Нам предстоит поговорить. = We have an important talk ahead of us / We need to talk.
• Мне предстоит работать всю ночь. = I have to work all night.

So there are two common patterns:

1. кому? + предстоит + noun

   • Нам предстоит трудный разговор.

2. кому? + предстоит + infinitive

   • Нам предстоит обсудить это.

Yes, it is very natural. It sounds a bit more serious, literary, or formal than a very plain everyday version.

Compare:

• Нам предстоит трудный разговор.
  Slightly weighty, serious, often used before an important or uncomfortable discussion.

• Нам нужно серьёзно поговорить.
  More direct: We need to talk seriously.

• У нас будет трудный разговор.
  More neutral: We’ll have a difficult conversation.

So the original sentence is perfectly natural, but it has a somewhat thoughtful or solemn tone.

Yes. Russian word order is flexible, though the basic version here is very natural:

• Нам предстоит трудный разговор.

Other orders are possible for emphasis:

• Трудный разговор нам предстоит.
• Предстоит нам трудный разговор.

These alternatives are more marked and depend on context. The neutral order for a learner to use is:

• Нам предстоит трудный разговор.

Here трудный means difficult in an emotional or practical sense. With разговор, it often suggests a conversation that will be:

• uncomfortable
• serious
• emotionally hard
• delicate

Possible close words:

• трудный разговор = difficult, hard conversation
• тяжёлый разговор = heavy, painful conversation
• сложный разговор = complex or difficult, sometimes a bit less emotional

So трудный разговор is very natural and broad. It can mean emotionally difficult, not just intellectually complicated.

Russian has no articles like a or the. So трудный разговор can mean:

• a difficult conversation
• the difficult conversation

The exact meaning depends on context.

In this sentence, English usually says:

• We have a difficult conversation ahead of us

But in some contexts it could also be:

• The difficult conversation is still ahead of us

Russian leaves that for the listener to infer.

Then the subject would become plural, and the verb and adjective would change to match it:

• Нам предстоят трудные разговоры.

Breakdown:

• предстоят = plural
• трудные разговоры = nominative plural

So the singular sentence is:

• Нам предстоит трудный разговор.

And the plural version is:

• Нам предстоят трудные разговоры.

This helps show that разговор is really the grammatical subject.

The stress is:

• предстои́т

And the full sentence is pronounced roughly like:

• Нам предстои́т тру́дный разгово́р.

Main stresses:

• нам
• предстои́т
• тру́дный
• разгово́р

Knowing the stress matters, because Russian stress is unpredictable and can change from form to form.