Learn Hardcore Chinese: dàjiā dōu dào le ma? wǒmen bā diǎn bàn chūfā ba. - Has everyone arrived? Let's set off at eight-thirty.

都 (dōu) means “all,” distributing the statement over the whole group. It emphasizes that the question concerns every member: “Have they all arrived?”
Without it, 大家到了吗？ still asks about everyone in context, but 都 makes the “all” explicit.
Alternatives with a stronger “everyone is present” idea: 大家都到齐了吗？ or 人都到齐了吗？

Why is 了 used after 到 in 到了吗? What aspect is it?

That 了 is the verb-suffix (perfective) 了, marking a completed event: “arrived (already/at some point).”
Compare:
- 到了 = arrived (this time; completed).
- 到过 = have (ever) been to; experiential.
Negation uses 没(有), not 不: 还没到, 没到 (not yet arrived). Saying 不到 here is wrong (it means “cannot reach/won’t reach”).

How do I answer this yes/no question naturally?

Can I say 到齐 instead of 到? What’s the nuance?

到齐 means “everyone is present; the group is complete.” It’s stronger than simple arrival.
大家都到了吗？ asks if everyone has arrived (individually).
大家到齐了吗？ asks whether the headcount is complete.

Why use 吗 here? Could I use 呢 or just 了吗?

吗 turns a statement into a neutral yes/no question.
V + 了 + 吗 is a common perfective yes/no pattern: 到(了)吗.
呢 does not form yes/no questions here; it’s used for “what about…?” or to indicate an ongoing state, e.g., 还没到呢 (“not yet”).
Without particles, 大家都到了？ (rising tone) sounds like seeking confirmation or mild surprise rather than a neutral query.

Where does the time go in 我们八点半出发吧? Can I move it or add 在?

Default word order: Subject + Time + Verb: 我们八点半出发吧.
You can front the time for emphasis: 八点半我们出发吧.
在 before a time is usually unnecessary in conversation. 我们在八点半出发 can appear in formal/announcing styles to mark “at (exactly) 8:30,” but everyday speech prefers no 在.

What does the final particle 吧 do in 出发吧?

Should I use 我们 or 咱们 for “let’s …”?

咱们 explicitly includes both speaker and listener(s) (“we all, including you”): 咱们八点半出发吧.
我们 is also fine; with 吧, context usually makes it inclusive.

How do I specify AM/PM for 八点半?

Add a time-of-day word before the hour (broad-to-narrow order):
- 上午八点半 / 下午八点半 / 晚上八点半
- For formality/precision: 上午八点三十分.

What’s the difference among 出发, 走, and 离开?

Can 都 move in the second sentence?

Rule: 都 must be before the verb it quantifies, though adverbs/time can sit between.
Both are acceptable: 我们都八点半出发吧 and 我们八点半都出发吧.
In practice, since 我们 already implies the whole group, most speakers just say 我们八点半出发吧.

How does negation interact with 都? What’s the difference between 都没 and 不都?

Can I drop 吗 and just use rising intonation?

大家都到了？ is common in speech but often seeks confirmation or shows mild surprise.
For a neutral yes/no, keep 吗 or use the A–N pattern: 到了没有？/ 到没到？

Can I add a place after 到?

Can I use 来 instead of 到 when asking about people’s arrival?

Yes: 大家都来了吗？ is natural. 来 focuses on “coming (to us/the event),” while 到 highlights “arriving/reaching (the place).” In many event contexts they’re interchangeable.

Any pronunciation pitfalls in this sentence?

Could I use 也 instead of 都?

No. 也 means “also/too” (additive), not “all.” 大家也到了吗？ would imply “Did they also arrive (in addition to someone else)?” which is odd here. Use 都 for “all.”