Learn Hardcore German: In unserer Nachbarschaft helfen sich Mieter und Mieterinnen oft gegenseitig. - In our neighborhood tenants male and tenants female often help each other.

Because in is a two-way preposition. With location (where?), it takes the dative. Nachbarschaft is feminine, and the feminine dative of the possessive unser- is unserer. So: in unserer Nachbarschaft. With movement (where to?), you’d use the accusative: e.g., in unsere Nachbarschaft ziehen (people move into our neighborhood).

What case is sich here, and why can helfen use it?

It’s dative. The verb helfen always takes a dative object (jemandem helfen). In the reciprocal use, the dative reflexive pronoun stands for “each other”: Sie helfen sich = “They help each other.” Dative reflexive forms:

ich: mir
du: dir
er/sie/es: sich
wir: uns
ihr: euch
sie/Sie: sich

Do I need both sich and gegenseitig? Isn’t that redundant?

You don’t strictly need both. Each of these is enough to express reciprocity:

Sie helfen sich (oft).
Sie helfen einander (oft).
Sie helfen (oft) gegenseitig. Adding gegenseitig can make the mutual idea extra explicit or emphatic. The combination sich gegenseitig is very common and natural.

Could I use einander instead of sich gegenseitig?

Yes. Mieter und Mieterinnen helfen einander oft is perfectly correct and a bit more compact. Don’t combine einander and gegenseitig together (e.g., einander gegenseitig)—that’s usually considered pleonastic.

Why is the verb helfen before the subject?

German main clauses are verb-second. The fronted phrase In unserer Nachbarschaft occupies position 1, so the finite verb helfen must be in position 2, and the subject Mieter und Mieterinnen follows after it: [1] In unserer Nachbarschaft | [2] helfen | [3+] sich Mieter und Mieterinnen …

Where does oft go? Can I move it?

Typical and natural: … helfen sich Mieter und Mieterinnen oft gegenseitig. You can also say … helfen sich oft gegenseitig … or, less commonly, … helfen sich gegenseitig oft. Frequency adverbs like oft usually come before manner-style adverbs like gegenseitig.

Do I have to say Mieter und Mieterinnen? Can’t Mieter mean everyone?

Traditionally, plural Mieter could be read as generic masculine. Many contexts now prefer gender-inclusive phrasing:

Pair: Mieterinnen und Mieter (order often female first in inclusive style)
Symbols: Mieter:innen, Mieter*innen (writing only)
Neutral forms: Mietende (increasingly used in admin/formal contexts) Your sentence uses an explicit pair, which is clear and inclusive.

Should there be an article: die Mieter und Mieterinnen?

Both are possible:

Without article: Mieter und Mieterinnen = tenants in general in that neighborhood (generic/habitual statement).
With article: die Mieter und Mieterinnen = the specific set of tenants (more definite, that known group). The original feels like a general observation.

Does helfen take the accusative? Why not jemanden helfen?

No—helfen takes the dative. Say jemandem helfen, never jemanden helfen. That’s why the reciprocal pronoun is dative sich here.

Can I use miteinander in this sentence?

Not with helfen in this meaning. Miteinander = “with each other/together” (good with verbs like arbeiten, sprechen). For mutual helping, use einander or (sich) gegenseitig:

✅ Sie helfen einander.
✅ Sie helfen sich gegenseitig.
❌ Sie helfen miteinander. (sounds odd)

Any quick pronunciation tips?

Mieter: ie is a long “ee” sound: MEE-ter.
Nachbarschaft: the ch is the harsh “ch” like in Scottish “loch”; stress on the first syllable: NACH-bar-….
gegenseitig: both g are hard “g”; sei sounds like English “zye”; final -ig is usually the “ich”-sound [ɪç] in standard German: ge-gen-ZAI-tɪç.
sich: “ich”-sound at the end [ɪç].
unserer: the unstressed vowels reduce; think “UN-ze-rer.”

What’s the nuance of Nachbarschaft vs. Viertel vs. Gegend?

Nachbarschaft: your immediate residential neighborhood/community feel.
Viertel: a (named) district/quarter of a city.
Gegend: area/region (looser, more geographical).

When would I use the accusative after in with this noun?

Use accusative for movement into the neighborhood:

Neue Leute ziehen in unsere Nachbarschaft. (accusative = movement) Use dative for location:
In unserer Nachbarschaft ist es ruhig. (dative = location)

Is gegenseitlich an alternative to gegenseitig?

Stick with gegenseitig. Gegenseitlich is rare/dated or regionally marked. In modern standard German, gegenseitig is the normal choice for “mutual.”