Learn Hardcore Chinese: tā hé tā dōu hěn gāoxìng.

They’re homophones: both are pronounced tā (first tone). In speech, you rely on context to know the gender. If you need to be explicit, speakers often specify with words like 男的 (male), 女的 (female), 那个男生/女生, or use names: e.g., 他和那个女生都很高兴. In writing, the characters differ, but in speech they sound the same.

What does 都 do here, and where must it go?

都 means “both/all” and distributes the predicate over a plural subject. It comes after the subject(s) it quantifies and before the predicate:

他和她都很高兴。
我们都喜欢咖啡。 It cannot go at the end of the sentence or before the subject by default.

Can I leave out 都? Is 他和她很高兴 correct?

Yes, 他和她很高兴 is grammatical and can mean “He and she are happy.” However, 都 is very commonly used to make the distributive meaning explicit and natural. Without 都, the sentence is still understandable, but 都 is preferred when emphasizing that each member of the group has the property.

Is 很 really “very” here? Why is it needed?

With predicate adjectives, Mandarin typically uses a degree adverb like 很 between the subject and the adjective. In neutral contexts, 很 often functions more like a grammatical linker than a strong “very.” So 他很高兴 is usually “He is happy.” If you truly want strong emphasis, use 非常/特别/极其 instead.

Why can’t I say 他是高兴?

Mandarin adjectives can directly serve as predicates; 是 links nouns, not adjectives. So you say 他很高兴 (He is happy). You can use 是 if the complement is a noun phrase: 他是个高兴的人 (He is a happy person). Bare 他是高兴 is odd unless in special contrastive or elliptical contexts.

Is 高兴 an adjective or a verb? How is it different from 开心?

高兴 is primarily an adjective meaning “happy/glad” and is common in set phrases like 很高兴认识你. It can also act verbally in some colloquial contexts (e.g., 我高兴就好), though “willing” is better expressed by 愿意/乐意.
开心 is also an adjective meaning “happy/cheerful.” In many contexts they’re interchangeable: 我很高兴/我很开心. Nuance: 高兴 often feels a bit more event/moment-focused or formal in greetings; 开心 can feel more casual and general.

Can I use 和 and 跟 interchangeably?

When linking nouns/pronouns (“A and B”), both are fine:

他和她都很高兴。
他跟她都很高兴。 跟 is a bit more colloquial; 和 is neutral. Neither 和 nor 跟 should be used to join whole clauses in the way English “and” does.

Can 和 connect entire clauses like “He is happy and she is happy”?

No. Don’t say 他很高兴和她很高兴. Use two clauses with a comma or an adverb:

他很高兴，她也很高兴。
他很高兴，而且她也很高兴。

Where exactly does 都 go if there are time or place words?

General order: Subject + time/place + 都 + predicate.

他们今天都很高兴。 (They are all happy today.)
他们在这里都很高兴。 (They are all happy here.) 都 still follows the subject (or the topicalized element it quantifies) and precedes the predicate.

How do I negate this sentence? What’s the difference between 都不 and 不都?

他和她都不高兴。 = Both of them are unhappy (unhappy applies to each).
他和她不都高兴。 = Not both are happy (at least one isn’t; maybe the other is). Also note degree nuances:
不高兴 = unhappy.
不很高兴 = not very happy (mild).
很不高兴 = very unhappy (strong).

How do I make the “very” truly strong?

Use a stronger degree adverb:

他和她都非常高兴。 (both are extremely/very happy)
他和她都特别高兴。
他和她都高兴极了。 (exuberant tone)

If I want to shorten it to “They are both happy,” what pronoun do I use for mixed genders?

Use 他们 for mixed or unspecified gender groups:

他们都很高兴。 Use 她们 only for all-female groups.

What about 俩? Can I say “The two of them are both happy”?

Yes. 俩 (liǎ) = “two (people).”

他们俩都很高兴。 (Both of them are happy)
他俩都很高兴。 (colloquial)

Any pronunciation tips for this sentence?

Tones: 他 tā (1), 和 hé (2), 她 tā (1), 都 dōu (1), 很 hěn (3), 高兴 gāoxìng (1–4).
很 is third tone; before a non–third tone, it’s often realized as a “half third” (low) in fluent speech.
兴 in 高兴 is fourth tone (xìng), not first (xīng). For x, keep the tongue tip down behind lower teeth; it’s a soft “sh” sound.

Does 都 mean they’re happy together, or each one is happy separately?

都 marks a distributive reading: each member of the group has the property. It does not by itself imply “together.” If you want “together,” add 一起: 他们都很高兴一起去。

What’s the difference between 也 and 都 in similar sentences?

也 = “also/too,” adds to a previous statement: 他很高兴，她也很高兴。
都 = “both/all,” quantifies a plural subject: 他们都很高兴。 You can combine them if the context warrants: 他们也都很高兴 = They are also all happy (in addition to some other group).