jokaga jamdeun dwie imorang samchoni geosireseo joyonghi iyagihaesseo.

조카 can mean either niece or nephew. Korean often does not mark gender in this word.

If you need to be specific, Korean can use:

• 여자 조카 = niece
• 남자 조카 = nephew

So in this sentence, 조카가 just means the niece/nephew depending on context.

가 is the subject marker, and here it marks 조카 as the subject of the first part of the sentence: 조카가 잠든 뒤에.

So the structure is basically:

• 조카가 잠들다 = the niece/nephew falls asleep
• 잠든 뒤에 = after falling asleep

Using 가 here is very natural because it simply identifies who fell asleep.

If you used 조카는, it would sound more like you are setting up the niece/nephew as a topic or contrast, such as:

• As for the niece/nephew, after they fell asleep...

That is possible in some contexts, but 조카가 is the most straightforward choice here.

잠든 comes from the verb 잠들다, which means to fall asleep.

Here, 잠든 is the adnominal form (the form used before a noun). It modifies 뒤:

• 잠든 뒤에
• literally: after having fallen asleep
• naturally: after the niece/nephew fell asleep

This pattern is very common:

• verb + -(으)ㄴ 뒤에 for past/completed actions
• 먹은 뒤에 = after eating
• 끝난 뒤에 = after it ended
• 잠든 뒤에 = after falling asleep

Why not the others?

• 잠들고 = and fell asleep / after falling asleep, but it links actions more loosely
• 잠들어서 = because fell asleep / after falling asleep, but it can also sound causal depending on context

잠든 뒤에 is especially clear for after X happened.

뒤에 means after in this sentence.

Literally, 뒤 means back or behind, but when used with a clause, it often means after:

• 식사한 뒤에 = after eating
• 집에 간 뒤에 = after going home
• 조카가 잠든 뒤에 = after the niece/nephew fell asleep

So this is a very useful time expression pattern:

• A-(으)ㄴ/는 뒤에 B
• After A, B

Yes. You could say:

• 조카가 잠든 후에 이모랑 삼촌이 거실에서 조용히 이야기했어.

This means almost the same thing.

The difference is mainly nuance:

• 뒤에 is very common and natural in everyday speech
• 후에 is also common, but can sound a bit more formal or written depending on context

In casual conversation, 뒤에 often feels more natural.

랑 means and or with in casual speech.

So:

• 이모랑 삼촌 = aunt and uncle

Then 이 marks the whole phrase as the subject:

• 이모랑 삼촌이 = the aunt and uncle (as subject)

This is a very common pattern in spoken Korean:

• 엄마랑 아빠가 왔어. = Mom and Dad came.
• 친구랑 내가 갔어. = My friend and I went.

Other similar connectors are:

• 하고 = and/with
• 와/과 = and/with, more formal or written

So you could also say:

• 이모하고 삼촌이
• 이모와 삼촌이

But 이모랑 삼촌이 sounds very natural and conversational.

Because 이모랑 삼촌 is treated as one combined noun phrase: aunt and uncle.

Then the subject marker is added to the whole phrase:

• 이모랑 삼촌이

You do not normally say:

• 이모가 삼촌이 for this meaning

That would sound like two separately marked subjects and would not be the normal way to say aunt and uncle together.

거실 means living room.

에서 marks the place where an action happens.

So:

• 거실에서 이야기했어
• talked in the living room

This is because 이야기하다 is an action, and 에서 is the normal particle for the location of an action:

• 학교에서 공부해요. = I study at school.
• 카페에서 만났어요. = We met at a cafe.
• 거실에서 이야기했어. = They talked in the living room.

If you used 거실에, it would usually suggest direction or existence rather than the location of the action.

조용히 is an adverb meaning quietly.

It comes from the adjective 조용하다 = to be quiet.

So:

• 조용히 이야기했어 = talked quietly

This is a very common adjective-to-adverb pattern:

• 조용하다 → 조용히 = quiet → quietly
• 천천하다 is not correct, but 천천히 = slowly
• 친절하다 → 친절히 = kindly (though 친절하게 is often more common)

In the sentence, 조용히 describes how they talked.

They are similar, but not always exactly the same.

• 이야기하다 = to talk, to have a conversation, to tell a story
• 말하다 = to speak, to say

In this sentence, 이야기했어 fits well because the aunt and uncle were having a quiet conversation.

Compare:

• 둘이 이야기했어. = The two of them talked.
• 그는 사실을 말했어. = He said the truth / He stated the fact.

So here, 이야기했어 sounds more natural than 말했어 because it suggests an exchange or conversation.

이야기했어 is in the casual informal style, often called 반말.

The polite version would be:

• 이야기했어요

So:

• 조카가 잠든 뒤에 이모랑 삼촌이 거실에서 조용히 이야기했어. = casual
• 조카가 잠든 뒤에 이모랑 삼촌이 거실에서 조용히 이야기했어요. = polite

Use 했어 with close friends, younger people, children, or in narration where casual style is appropriate. Use 했어요 in most everyday polite situations.

Because Korean is basically a Subject-Object-Verb language, and the main verb normally comes at the end of the clause or sentence.

So the sentence builds up like this:

• 조카가 잠든 뒤에 = after the niece/nephew fell asleep
• 이모랑 삼촌이 = the aunt and uncle
• 거실에서 = in the living room
• 조용히 = quietly
• 이야기했어 = talked

English often puts things earlier or in a different order, but Korean usually saves the main verb for the end.

Normally, 이모랑 삼촌이 means one aunt and one uncle.

Korean nouns usually do not mark singular vs. plural unless needed. So technically context matters, but the most natural reading is:

• the aunt and uncle

If the speaker wanted to make plurality clearer in another situation, they might add context or use plural markers, but here the simple reading is one aunt plus one uncle.

Not always.

Literally:

• 이모 = mother’s sister
• 삼촌 = uncle, often a younger male relative, but in everyday use it can be broader

In real life, Koreans also sometimes use these family terms for familiar adults, especially when speaking to children.

So depending on context, this sentence could refer to:

• the child’s real aunt and uncle, or
• adults being called aunt and uncle in a family-like way

But without extra context, learners usually understand them first as family members.

The sentence has two parts:

1. 조카가 잠든 뒤에

   • 조카가 = the niece/nephew
   • 잠든 = having fallen asleep
   • 뒤에 = after

2. 이모랑 삼촌이 거실에서 조용히 이야기했어

   • 이모랑 삼촌이 = the aunt and uncle
   • 거실에서 = in the living room
   • 조용히 = quietly
   • 이야기했어 = talked

So the full pattern is:

• [After X happened], Y did something.

That is a very common Korean sentence structure.