wǒ yéye nǎinai xǐhuan zài jiāoqū sànbù, shuō nàli de kōngqì bǐ chéngli xīnxiān, rén yě bú nàme yōngjǐ.

Yes. In this sentence, 我爷爷奶奶 means my grandpa and grandma, or more naturally, my grandparents.

Chinese often puts close family terms together like this:

• 爸爸妈妈 = mom and dad
• 哥哥姐姐 = older brother and older sister
• 爷爷奶奶 = grandfather and grandmother

If you really wanted to say my grandfather’s grandmother, you would normally need a clearer structure, such as 我爷爷的奶奶.

Because Chinese often lists closely connected people or common pairs without 和.

So both of these work:

• 爷爷奶奶 = grandpa and grandma
• 爷爷和奶奶 = grandpa and grandma

Without 和, it sounds compact and very natural, especially for family pairs.

The second syllable is a neutral tone.

Many repeated family words in Mandarin work this way:

• 爸爸 = bàba
• 妈妈 = māma
• 爷爷 = yéye
• 奶奶 = nǎinai

So the first syllable carries the main tone, and the second is lighter and shorter.

Literally, it is something like like to walk in the suburbs.

The pattern is:

喜欢 + 在 + place + verb

So:

• 喜欢 = like
• 在郊区 = in the suburbs
• 散步 = take a walk / go for a walk

Chinese usually puts the location before the action:

• 在公园散步 = take a walk in the park
• 在家吃饭 = eat at home

In this sentence, it functions as a verb, meaning to take a walk or to go for a walk.

You can use it like other verbs:

• 我喜欢散步。 = I like taking walks.
• 我们去散步吧。 = Let’s go for a walk.

It is often taught as a verb, though historically it is a verb-object type expression.

The comma links another clause to the first one. The person doing the speaking is still 我爷爷奶奶.

So the full meaning is:

My grandparents like walking in the suburbs, and they say...

Chinese often omits a repeated subject when it is already clear. A fuller version would be:

我爷爷奶奶喜欢在郊区散步，他们说那里的空气比城里新鲜。

But repeating 他们 is not necessary.

那里 means there, and 那里的空气 means the air there.

Here, 的 links 那里 to 空气:

• 那里 = there
• 那里的 = of that place / there’s
• 那里的空气 = the air there

This is a very common pattern:

• 这里的老师 = the teachers here
• 学校的图书馆 = the school’s library
• 北京的冬天 = Beijing’s winter

The basic comparison pattern is:

A 比 B + adjective

So:

• 那里的空气 = the air there
• 比城里 = compared with the city
• 新鲜 = fresh

Together: The air there is fresher than in the city.

A more expanded version would be:

• 那里的空气比城里的空气新鲜

But Chinese often leaves out repeated words when the meaning is obvious.

Because with 比 comparisons, Chinese usually uses the adjective directly:

• A 比 B 新鲜
• A 比 B 大
• A 比 B 便宜

You normally do not need 很 there.

So:

• 那里的空气比城里新鲜 = correct
• 那里的空气比城里很新鲜 = not the normal basic pattern

If you want extra emphasis, you might use 更 instead:

• 那里的空气比城里更新鲜 = The air there is even fresher than in the city.

Literally, 城里 means inside the city, but in modern Mandarin it often just means in the city, the urban area, or sometimes downtown, depending on context.

It is very common in everyday speech, especially when contrasting with places like:

• 郊区 = suburbs
• 乡下 = the countryside

So in this sentence, 城里 is simply the opposite of 郊区.

This is because of tone sandhi.

Normally, 不 is fourth tone: bù. But when it comes before another fourth-tone syllable, it changes to second tone: bú.

Here it comes before 那 in 那么:

• 那 = nà = fourth tone

So:

• 不那么 is pronounced bú nàme

This is the same rule as in:

• 不是 = bú shì
• 不对 = bú duì

也 means also or too.

The sentence first gives one reason:

• the air is fresher

Then it adds another:

• 人也不那么拥挤 = people are also not so crowded / it’s also not so crowded

So 也 shows an additional point:

• 空气更好，人也不那么拥挤
• The air is better, and it’s also less crowded.

In Chinese, words like 也 usually come after the subject and before the rest of the predicate.

It means not so crowded or not as crowded.

• 那么 here refers to that degree / so much
• 不那么拥挤 = not that crowded / not so crowded

In context, the comparison is with 城里, so the idea is:

• it’s not as crowded as the city

A more explicit version would be:

• 没有城里那么拥挤 = not as crowded as the city

But 不那么拥挤 sounds natural when the comparison is already understood.

Yes, it is understandable and acceptable. The idea is that people are not packed together so tightly there.

That said, in English we usually translate it more naturally as:

• it’s also less crowded
• there are also fewer crowds

In Chinese, you may also hear slightly different versions, such as:

• 那里也没那么拥挤。
• 那里的人也没那么多。

So the original sentence is fine, but the English translation will often sound smoother if you make the place rather than the people the subject.