ano hutago ha huku made onazi de, hontou ni sokkuri desu.

あの is a demonstrative word meaning that / those over there.

So:

• あの双子 = those twins
• more literally, that pair of twins over there

A useful comparison:

• この = this
• その = that
• あの = that over there

In this sentence, あの is directly modifying the noun 双子.

双子 means twins as a pair. Japanese often treats it as a single unit meaning the twin pair.

So:

• あの双子は = as for those twins...

Even though it refers to two people, the grammar works just like with a normal noun phrase.

This is similar to how English can sometimes treat a couple or a pair as one unit.

は marks the topic.

So あの双子は means:

• as for those twins, ...
• those twins, ...

It tells you what the sentence is about.

The rest of the sentence then comments on them:

• 服まで同じで、本当にそっくりです
• even their clothes are the same, and they really look alike

That is a very natural question.

Yes, a fuller version could be:

• あの双子は、服まで同じで...
• understood as those twins are such that even their clothes are the same

You do not need 双子の服 here because 服 is not directly being used as the twins’ clothes inside one noun phrase. Instead, it is part of the predicate:

• 服まで同じ = even their clothes are the same

The ownership is understood from context: we are talking about the twins, so 服 naturally means their clothes.

Japanese often leaves out possessive words when they are obvious.

Here, まで means even.

So:

• 服まで同じ = even their clothes are the same

It adds a sense of surprise or emphasis. The speaker is saying the similarity goes very far — not only do the twins look alike, but even their clothes match.

This is different from the common meaning of まで as until.
For example:

• 3時まで = until 3 o’clock

In this sentence, it is the even meaning.

同じ means same, and it behaves somewhat like an adjective, but it is a little special in Japanese.

In this sentence:

• 服まで同じ = even their clothes are the same

You can think of 同じ here as describing 服.

It does not behave exactly like a regular い-adjective, and learners often just memorize common patterns such as:

• A は B と同じです = A is the same as B
• 服が同じ = the clothes are the same

So here, 同じ is simply being used in the very common sense of the same / identical.

The で here connects 同じ to the next part of the sentence.

So:

• 服まで同じで、本当にそっくりです
• even their clothes are the same, and they really look alike

You can think of this で as a linking form, similar to:

• and
• being
• with ... being ...

A more literal feel is:

• their clothes being the same as well, they really look alike

This で is a very common way to join clauses in Japanese.

The comma marks a pause between two connected parts:

• 服まで同じで
• 本当にそっくりです

It helps readability and shows that the first part leads into the second.

Japanese commas are often used more flexibly than English commas, so they do not always match English punctuation exactly.

本当に means really or truly.

It emphasizes そっくりです:

• 本当にそっくりです = they really look alike

The base word is 本当 meaning truth / real / genuine, and 本当に is its adverb form.

Compare:

• 本当です = it is true
• 本当に似ています = they really resemble each other
• 本当にそっくりです = they really look exactly alike

This is an important distinction.

• 同じ = the same
• そっくり = extremely alike / almost identical in appearance

In this sentence:

• 服まで同じ = even their clothes are the same
• 本当にそっくりです = they really look exactly alike

So 同じ talks about actual sameness, while そっくり talks about strong resemblance.

For example:

• 同じ服 = the same clothes
• そっくりな顔 = very similar faces

Using both together makes the sentence stronger: they resemble each other so much that even their clothes are the same.

そっくり can be used directly as the predicate with です:

• そっくりです = are very much alike

When it comes before a noun, it can use な:

• そっくりな二人 = two people who look very alike

So:

• before a noun: そっくりな + noun
• at the end of a sentence: そっくりです

That is why そっくりです is correct here.

Yes. A fairly literal version would be:

• As for those twins, even their clothes are the same, and they really are exactly alike.

A more natural English translation would be:

• Those twins really look alike — even their clothes are the same.

Or:

• Those twins are so alike; even their clothes are the same.

It breaks down like this:

• あの双子は
  As for those twins,

• 服まで同じで、
  even their clothes are the same, and...

• 本当にそっくりです。
  they really look alike.

So the overall pattern is:

• Topic + description 1 + connective + description 2

This is a very common Japanese sentence pattern.