jīntiān zhè jiā kāfēiguǎn jì ānjìng yòu gānjìng.

Here 家 (jiā) is a measure word (classifier), not the noun “home”.

In Chinese, many places of business or organizations use 家 as their measure word:

• 一家咖啡馆 – one café
• 一家饭店 – one restaurant
• 一家银行 – one bank
• 一家公司 – one company

So 这家咖啡馆 literally means “this [one] café”, and that’s the natural way to say “this café” in Chinese. Using 家 here sounds much more natural than 个 for a café/shop/restaurant.

You can hear 这个咖啡馆 in casual speech, and people will understand you, but:

• 这家咖啡馆 is the most natural and standard way to refer to “this café”.
• 这个咖啡馆 sounds a bit less idiomatic, because cafés are businesses, and the usual classifier for such places is 家, not 个.

So:

• Preferred: 这家咖啡馆
• Understandable but less natural: 这个咖啡馆

Both are possible, but the nuance changes slightly.

1. 今天这家咖啡馆既安静又干净。

   • The phrase 今天这家咖啡馆 is one big noun phrase: “this café today”.
   • It subtly contrasts today’s state of this café with how it might usually be, or with other days:
     → “Today, this café is (unusually) both quiet and clean.”

2. 这家咖啡馆今天既安静又干净。

   • Here, 这家咖啡馆 is the subject, and 今天 is a time adverb inside the predicate:
     “This café today is both quiet and clean.”
   • The meaning is very close; this one sounds a bit more neutral in focus.

Chinese commonly puts time expressions early, so both orders are acceptable. Your original sentence is very natural.

既…又… is a fixed pattern meaning “both … and …” for two parallel qualities or actions.

In this sentence:

• 既安静又干净 = “both quiet and clean”

It’s used when the two parts are of the same grammatical type (both adjectives, both verbs, etc.):

• 这本书既有意思又有用。
  “This book is both interesting and useful.”
• 他既会说中文又会说日文。
  “He can speak both Chinese and Japanese.”

They all express “X and also Y”, but with different flavors:

1. 既…又…

   • Slightly bookish / formal, but also used in everyday speech.
   • Symmetrical, neat, often used in writing and careful speech.
   • Example: 既安静又干净 – both quiet and clean.

2. 又…又…

   • Very common and colloquial.
   • Meaning is almost the same as 既…又… in many contexts.
   • You could also say: 今天这家咖啡馆又安静又干净。
     This is perfectly natural.

3. 不但…而且…

   • Often translates as “not only … but also …”.
   • Slightly more emphasis that Y is an extra or unexpected positive/negative point.
   • Example: 这家咖啡馆不但安静，而且很干净。
     “This café is not only quiet, but also very clean.”

So here, you could use 既…又…, 又…又…, or 不但…而且…, but the tone and emphasis shift slightly.

Chinese does not always need 是.

• 是 is mainly used to link nouns / noun phrases:
  
  • 他是老师。– He is a teacher.
  • 这是咖啡馆。– This is a café.

With adjectives as predicates, the usual pattern is:

• Subject + (degree word, often 很) + adjective
  
  • 咖啡馆很安静。– The café is quiet.

When you use patterns like 既…又…, that whole structure is the predicate, so you don’t insert 是:

• 今天这家咖啡馆既安静又干净。 ✅
  Adding 是 – 今天这家咖啡馆是既安静又干净 – sounds unnatural in normal speech.

Normally, no; that sounds clumsy.

In a 既…又… structure, you typically do not add 很 or other degree adverbs:

• Natural: 既安静又干净 ✅
• Awkward: 既很安静又很干净 ❌ (possible only in very marked/emphatic style)

The pattern itself already presents the qualities in a balanced way, so extra degree markers are usually dropped.

Words like 安静 and 干净 are often called stative verbs or adjectives in grammar discussions. The key idea:

• They describe a state (“to be quiet”, “to be clean”).
• In Chinese, such words can function as the predicate directly, without 是.

In 既安静又干净:

• 安静 = “(is) quiet”
• 干净 = “(is) clean”

So the whole thing is effectively “is both quiet and clean”, but Chinese does not need an explicit “to be”.

You can’t just put 不 in front of 既 in a simple way; instead, you change the structure:

1. Not quiet but (still) clean

   • 今天这家咖啡馆不安静，但是很干净。
   • “Today this café is not quiet, but it is clean.”

2. Neither quiet nor clean

   • 今天这家咖啡馆既不安静，也不干净。
   • Pattern: 既不…也不… = “neither … nor …”

So for negative “both … and …”, you often see 既不…也不….

In this sentence, 今天 most naturally means “today (this particular day)”.

• 今天这家咖啡馆既安静又干净。
  → “Today, this café is (both) quiet and clean.”

If you wanted the meaning “nowadays / these days, this café is quiet and clean”, you’d more typically phrase it differently, for example:

• 这家咖啡馆现在既安静又干净。
• 这家咖啡馆这段时间都很安静，也很干净。

So here, it’s about today’s situation, not a long-term trend.

既 appears in a few patterns:

1. 既…又… – “both … and …” (your sentence)

   • 这家咖啡馆既安静又干净。

2. 既…也… – similar, a bit less common than 既…又…

   • 这家咖啡馆既安静也干净。

3. 既然… (就/那/那么)… – “since / now that … (then) …”

   • 既然你来了，就进来坐坐吧。
     “Since you’re here, then come in and sit for a bit.”

In your sentence, 既 is the first half of the 既…又… “both … and …” pair.