Learn Hardcore Swedish: Jag tror att hennes familj kommer snart, och jag hoppas att de stannar. - I think that her family is coming soon, and I hope that they stay.

Swedish often uses present tense to talk about the near future, especially for plans and expected events. Jag tror att hennes familj kommer snart = I think her family is coming/arriving soon.

ska highlights intention or a plan: Jag tror att hennes familj ska komma snart (there’s a plan for them to come).
kommer att + infinitive is a neutral prediction: Jag tror att hennes familj kommer att komma snart (grammatical but clunky with two forms of komma, so most people avoid it here and just use present: kommer).

Do I have to keep the word att after tror and hoppas?

In careful writing, yes—keep att. In everyday speech, it’s common to drop it after verbs like tro, tycka, hoppas:

Spoken: Jag tror (att) de kommer snart. Jag hoppas (att) de stannar.
Written standard (and safest): Jag tror att … Jag hoppas att …

Is the comma before och necessary?

It’s optional here. Swedish generally does not require a comma before och when joining two main clauses, but writers sometimes add one to mark a pause or improve readability. Both are fine:

Jag tror att …, och jag hoppas att …
Jag tror att … och jag hoppas att …

Why is it hennes familj and not hennes familjen?

Possessive pronouns in Swedish take an indefinite noun. So you say:

hennes familj, min bil, vår lägenhet Never add the definite ending with a possessive:
Not: hennes familjen, min bilen. With adjectives it’s still indefinite: hennes stora familj.

Why de and not dem in att de stannar?

De is the subject form; dem is the object form. In the clause att de stannar, the pronoun is the subject of stannar, so it must be de.

Subject: De stannar.
Object: Jag träffar dem i morgon. Note: In most speech both are pronounced dom, but in standard writing you still use de/dem.

If familj is singular, why refer back with de (they) instead of den (it)?

Swedish often uses de for collective nouns that refer to people (e.g., familj, klass, personal) to emphasize the individuals. Using den treats the group more as a single unit; with people, de is more natural:

Hennes familj … Jag hoppas att de stannar.

Why is the word order att hennes familj kommer snart and not att kommer hennes familj snart?

Swedish main clauses are V2 (the finite verb is in second position), but subordinate clauses are not. After att, the usual order is:

att + subject + (sentence adverb) + finite verb + … So: att hennes familj kommer snart is correct. You do not invert to att kommer hennes familj …

Where should snart go? Can I say att hennes familj snart kommer?

Default and most natural in a subordinate clause is after the finite verb: att hennes familj kommer snart. You may sometimes see att hennes familj snart kommer for stylistic emphasis, but the neutral choice is kommer snart. Don’t front it with inversion in a subclause.

Should it be hoppas att or hoppas på att?

With a full clause, hoppas att is the standard choice: Jag hoppas att de stannar.
Use hoppas på before a noun: Jag hoppas på fint väder.
You will hear hoppas på att in speech and writing; it’s common and accepted, but many style guides prefer plain hoppas att before a clause.

What’s the nuance difference between stannar, stanna kvar, and stanna över?

stannar = stay (or stop) in general: Jag hoppas att de stannar.
stanna kvar = stay on/remain (stronger sense of not leaving): Jag hoppas att de stannar kvar.
stanna över (often with a time period) = stay over: De stannar över natten.

When should I use tror vs tycker for I think?

tror = belief about facts/what you expect will happen: Jag tror att hennes familj kommer snart.
tycker = opinion/judgment: Jag tycker att hennes familj är trevlig. English I think covers both, but Swedish separates them.

Why hennes and not sin/sitt/sina here?

hennes is the non‑reflexive possessive for she/her. sin/sitt/sina is reflexive and refers back to the subject of the same clause. In Jag tror att hennes familj kommer, the subject of the subordinate clause is hennes familj, not the person referred to by hennes. You cannot use sin here; among other things, sin cannot be used in (or as part of) the subject of a clause. So hennes familj is the correct (and only) choice.

Could I say ankommer or anländer instead of kommer?

kommer is the everyday, general verb for come/arrive and is perfect here.
ankommer and anländer are more formal and are used especially for scheduled arrivals (trains, flights). Example: Tåget anländer kl. 17.42.
For people casually coming soon, stick with kommer.

Do I have to repeat att before each clause, or can one att cover both?

Each subordinate clause needs its own att. In your sentence, there are two separate clauses:

[att hennes familj kommer snart]
[att de stannar] So you repeat att.

Can I omit the second jag after och?

Yes, you can. Both are fine:

With repetition: Jag tror att …, och jag hoppas att …
Without repetition: Jag tror att … och hoppas att … Omitting the repeated subject is common and natural when it’s the same subject.

Any pronunciation tips for tricky words here?

Jag is often pronounced like “ya” in casual speech.
och is commonly just “o” (the ch is usually silent).
familj ends with a palatalized sound, like “fa-MIL-y”.
de is pronounced “dom” in most dialects.
kommer has a short o (like in English “cot” for many speakers).
stannar has a doubled n sound; both syllables are clearly pronounced.