Learn Hardcore German: In einer guten Partnerschaft bleiben beide tolerant, auch wenn sie nicht immer der gleichen Meinung sind. - In a good partnership both remain tolerant even when they are not always of the same opinion.

Accusative = movement into something
- Ich gehe in eine gute Partnerschaft. – I’m going into a good partnership.
Dative = location / state in something
- In einer guten Partnerschaft bleiben beide tolerant. – In a good partnership, both remain tolerant.

Here we’re talking about the state within a partnership, not movement into it, so dative is used: in einer guten Partnerschaft.

Why is the adjective ending guten in einer guten Partnerschaft?

Partnerschaft is:

feminine
singular
in the dative case (because of in with “location” meaning)
with the indefinite article (einer)

In dative singular, all genders with an article take -en on the adjective:

in einem guten Auto (neuter, dative)
in einem guten Restaurant (neuter, dative)
in einem guten Verein (masc., dative)
in einer guten Partnerschaft (fem., dative)

So guten is the regular dative singular adjective ending after einer.

Why is it bleiben tolerant and not just sind tolerant?

Both are grammatically correct, but they express slightly different nuances:

sind tolerant – “are tolerant” (describes a state)
bleiben tolerant – “remain / stay tolerant” (emphasizes continuity despite something)

In this sentence:

In einer guten Partnerschaft bleiben beide tolerant, auch wenn ...

the idea is that in a good partnership, the partners continue to be tolerant even when they disagree. Bleiben fits the “even then / still” idea better.

Why is it beide tolerant and not beiden tolerant?

Here beide is the subject of the sentence:

... bleiben beide tolerant ...

Subject = nominative case.
Nominative plural form is beide, not beiden.

Beide bleiben tolerant. – Both stay tolerant. (nominative)
Ich helfe beiden. – I help both. (dative plural)

So we use beide because it’s nominative plural.

In auch wenn sie nicht immer der gleichen Meinung sind, why does sind go at the end?

Because wenn introduces a subordinate clause in German. In subordinate clauses, the finite verb goes to the end:

Main clause: Sie sind nicht immer derselben Meinung.
Subordinate clause with wenn: ... wenn sie nicht immer derselben Meinung sind.

So:

wenn (subordinating conjunction) → sends the verb to final position
therefore sind is placed at the end of the clause.

What is the difference between auch wenn and obwohl here? Could I say obwohl sie nicht immer der gleichen Meinung sind?

You could say obwohl, and the sentence would still be correct:

... bleiben beide tolerant, obwohl sie nicht immer der gleichen Meinung sind.

But there is a nuance:

obwohl ≈ “although / even though” – fact that contrasts with the main clause
auch wenn ≈ “even if / even though” – often allows more of a hypothetical or general, rule-like sense

In this sentence, auch wenn suggests a more general rule:

In a good partnership, both stay tolerant, even when / even if they are not always of the same opinion.

It sounds a bit more generic than obwohl, which feels more like referring to specific, known disagreements.

Who or what does sie refer to in auch wenn sie nicht immer der gleichen Meinung sind?

Sie here is 3rd person plural and refers back to beide:

In einer guten Partnerschaft bleiben beide tolerant, auch wenn sie nicht immer der gleichen Meinung sind.

So sie = “the two partners” / “both of them”.

You can see this from the verb sind (plural), which matches plural sie. If it were singular sie, the verb would be ist.

What case is der gleichen Meinung, and why is it der and not die?

The phrase der gleichen Meinung sein is (traditionally) a genitive construction that describes a quality:

derselben Meinung sein / der gleichen Meinung sein – literally “to be of the same opinion”

For Meinung (feminine, singular), the genitive singular article is der:

genitive singular feminine: der
dative singular feminine: der
nominative / accusative singular feminine: die

So:

die Meinung (nom.)
der Meinung (gen.)
der Meinung (dat.)

Here it’s genitive (“of which opinion? of the same opinion”), and genitive feminine singular uses der, not die. The form just happens to be identical to dative feminine singular.

Why does the adjective in der gleichen Meinung also end in -en?

In the genitive singular with a definite article, all adjectives take -en, regardless of gender:

des guten Mannes (masc., gen.)
des guten Kindes (neuter, gen.)
der guten Frau (fem., gen.)
der gleichen Meinung (fem., gen.)

So gleichen is the regular adjective ending in genitive singular with a definite article (der).

Why is it nicht immer der gleichen Meinung and not immer nicht der gleichen Meinung?

Word order with nicht can change the meaning slightly.

nicht immer = “not always”
→ sometimes yes, sometimes no
Sie sind nicht immer der gleichen Meinung.
They are not always of the same opinion.
immer nicht would mean something like “still not / always not” and is much less usual here and would sound odd in this context.

The intended meaning is that they sometimes disagree, not that they are constantly of a different opinion. Therefore, nicht goes directly before immer: nicht immer.

Could we also say derselben Meinung instead of der gleichen Meinung? Is there a difference?

Yes, you can absolutely say:

... auch wenn sie nicht immer derselben Meinung sind.

Both are correct:

derselben Meinung – more idiomatic, very common set phrase
der gleichen Meinung – also correct, maybe a bit more literal / less idiomatic

Meaning-wise, in this context they are practically the same: to be of the same opinion.

Why is Meinung singular here and not Meinungen?

German typically uses the singular in the idiom:

(nicht) derselben / der gleichen Meinung sein

Literally: “to be (not) of the same opinion.”
This refers to the stance on a particular issue, not to multiple separate opinions at once.

So even if there are two people, they either share one opinion on a given matter or they don’t; therefore Meinung stays singular.