Learn Hardcore Japanese: ani ha kaigai no zeikin no nyuusu wo yomi, syakai no henka wo tyousasimasita. - My older brother read news about taxes overseas and researched social changes.

は marks the topic: 兄は… = “As for my older brother,…”
が marks the subject and often answers a “who?” question or adds focus/contrast: 誰が読みましたか。— 兄が読みました。
Using 兄は simply sets the scene; 兄が highlights that it was the brother (not someone else).

What’s happening with the double の in 海外の税金のニュース? Which word is the main noun?

This is a modifier chain. The rightmost noun is the head.
Structure: [海外の [税金の [ニュース]]] = “news about taxes related to overseas.”
So ニュース is the main noun; everything before it narrows down what kind of news.

Does 海外の税金のニュース mean “news from overseas about taxes” or “news about overseas taxes”?

By default it reads as “news about overseas taxes.”
If you mean “overseas media’s news about taxes,” clarify:
- “Overseas taxes” sense: 海外の税金に関するニュース / 海外の税制に関するニュース
- “Overseas media” sense: 海外のニュースで取り上げられた税金の話題

Why is 読み、 used instead of 読んで? Are they different?

読み、 is the polite/written way of linking clauses with the verb’s ます-stem (連用形). It feels formal and concise.
読んで (て-form) is the standard spoken connector.
Meaning is the same here: both “read (and then) ….”

Is the comma after 読み required, and what is this grammar called?

This is called 連用中止 (linking with the ます-stem and “stopping” the sentence midstream).
The comma 、 isn’t grammatically required but is normal for readability in writing.

Is ニュースを読む natural? Should it be ニュースを見る?

Why を with 調査しました? Can I say について instead?

Xを調査する treats X as the direct object of a systematic investigation (more formal).
Xについて調査する means “investigate about X,” slightly broader/looser.
Both are fine; を feels tighter and more direct.

What’s the difference between 調べる, 調査する, and 研究する?

Is it okay that the first verb isn’t in ます-form even though the sentence ends in 調査しました?

Yes. In Japanese, only the final predicate needs to show politeness. The earlier 読み、 (ます-stem) is already a formal linking form. You could also say 読んで、調査しました.

Why 兄 and not お兄さん? Can I use お兄さん here?

Refer to your own older brother as 兄 in neutral/polite contexts.
お兄さん is for someone else’s older brother, or when addressing your brother (family talk: お兄ちゃん).
Saying お兄さんは… about your own brother to outsiders can sound childish or odd.

Do I need to say 私の before 兄 to mean “my older brother”?

Usually no. 兄 by default means your own older brother. Use 私の兄 only to disambiguate if needed.

Can I reorder it and say 税金の海外のニュース?

That’s unnatural for “news about overseas taxes.” Keep the chain 海外の税金のニュース.
If you really mean “overseas news (media) about taxes,” rephrase: 海外のニュースで取り上げられた税金の話題.

How do you pronounce the whole sentence?

Kana: あにはかいがいのぜいきんのニュースをよみ、しゃかいのへんかをちょうさしました。
Romaji: Ani wa kaigai no zeikin no nyūsu o yomi, shakai no henka o chōsa shimashita.

What’s the nuance difference among 海外, 外国, and 国外?

Is 変化 the best word here? How is it different from 変更 or 変動?

Does the sentence imply a sequence (first read, then researched) or just list actions?

With 読み、 it typically implies sequence: read first, then investigated.
It can also feel like a concise list in expository writing, but here “sequence” is the natural reading.

Can I connect the clauses with そして or use と to join them?

そして is acceptable: ニュースを読み、そして社会の変化を調査しました, but it can be wordy alongside 、.
と doesn’t join verbs in this “and then” sense. Use 読んで or the ます-stem link (読み、).

Would 税制 be more precise than 税金 here?

税金 = taxes (the money/levies).
税制 = the tax system/policy.
If the news is about policy/reform, 税制（改正）のニュース or 税制に関するニュース is more precise. Otherwise 税金のニュース is fine.

Is it okay to have two を in one sentence (ニュースを and 変化を)?

Yes. Each verb takes its own direct object: ニュースを読む and 変化を調査する. This is completely normal.