La narradora cuenta la historia con mucha naturalidad, y el diálogo entre las hermanas suena real.

Because contar is the usual verb for telling a story.

• contar una historia = to tell a story
• decir = to say

So:

• La narradora cuenta la historia = the narrator tells the story
• La narradora dice la historia would sound unnatural in most contexts

Spanish often uses contar for stories, jokes, anecdotes, and events.

Narradora is the feminine form of narrador.

• el narrador = the male narrator
• la narradora = the female narrator

Spanish usually marks the gender of people with nouns like this:

• profesor / profesora
• escritor / escritora
• narrador / narradora

So this sentence tells you that the narrator is female.

Spanish uses definite articles (el, la, los, las) more often than English does.

Here:

• la historia = the story
• el diálogo = the dialogue

Even when English might sometimes leave out the, Spanish often keeps it. In this sentence, the speaker is referring to a specific story and a specific dialogue, so the articles sound natural and expected.

It is a prepositional phrase:

• con = with
• mucha = a lot of / much
• naturalidad = naturalness

So literally it means with a lot of naturalness, although in natural English we would usually say something like very naturally.

The full idea is that the narrator tells the story in a very natural way.

Because muy modifies adjectives and adverbs, while mucho/a modifies nouns.

Here, naturalidad is a noun, so you need mucha:

• mucha naturalidad = a lot of naturalness

Compare:

• muy natural = very natural
• muy naturalmente = very naturally
• mucha naturalidad = a lot of naturalness

Also, mucha is feminine singular because naturalidad is feminine singular.

Yes, you could say La narradora cuenta la historia muy naturalmente or de manera natural, but con mucha naturalidad is very common and sounds smooth and idiomatic.

There is a slight stylistic difference:

• con mucha naturalidad sounds a bit more descriptive and polished
• naturalmente is shorter and more direct

Spanish often likes noun phrases like con naturalidad, con claridad, con emoción, etc.

Literally, suena real means sounds real.

Spanish uses sonar not only for actual sound, but also for how something seems or comes across, just like English:

• Eso suena bien = That sounds good
• Suena raro = It sounds strange
• Suena real = It sounds real

So here, el diálogo entre las hermanas suena real means the dialogue feels believable or authentic.

Both words exist, but they are not exactly the same.

• real = real, genuine, believable
• realista = realistic

In this sentence, suena real is very natural Spanish and means the dialogue feels authentic.

You could also hear suena realista, but suena real is simpler and very common when talking about whether speech, reactions, or characters feel believable.

It means between the sisters or among the sisters, depending on context.

• entre = between / among
• las hermanas = the sisters

Since there are sisters interacting with each other, el diálogo entre las hermanas means the dialogue that happens between them.

Spanish uses entre in both senses:

• entre dos personas = between two people
• entre amigos = among friends

Spanish often leaves out possessives when the relationship is clear from context.

So instead of saying:

• el diálogo entre sus hermanas

it often just says:

• el diálogo entre las hermanas

This sounds more natural when the reader already knows which sisters are being discussed. Spanish prefers the article where English might use his, her, or their.

Because diálogo is stressed on the third-to-last syllable:

• di-á-lo-go

Words stressed on the third-to-last syllable are called esdrújulas, and in Spanish they always take a written accent.

So:

• diálogo needs the accent mark on á

The accent helps show the correct pronunciation.

Yes, it is very normal.

The structure is:

• La narradora = subject
• cuenta = verb
• la historia = direct object
• con mucha naturalidad = adverbial phrase describing how she tells it

So it follows a very common Spanish pattern:

subject + verb + object + extra information

It is straightforward and natural, which is one reason this sentence is good for learners.

Because y means and and joins the two parts of the sentence:

• La narradora cuenta la historia con mucha naturalidad
• el diálogo entre las hermanas suena real

Together they describe two positive qualities of the writing.

As a side note, y changes to e before words beginning with an i sound, but that does not happen here because the next word is el, not an i sound word.