Dans notre groupe, nous nous aidons les uns les autres quand le cours devient difficile.

They do two different jobs:

• The first nous is the subject pronoun: we
• The second nous is the object pronoun tied to the pronominal verb s'aider

So nous nous aidons literally looks like we help ourselves, but with a plural subject it often has a reciprocal meaning: we help each other.

This is very common in French:

• Nous nous parlons = we talk to each other
• Ils se connaissent = they know each other

Les uns les autres means each other or one another.

It is a reciprocal expression used to make the mutual idea very clear. In this sentence, it reinforces the idea that the people in the group help one another, not just themselves individually.

A closely related form is:

• l'un l'autre = each other / one another, often for two people
• les uns les autres = each other / one another, for more than two people

Good question. It is not strictly necessary, but it adds:

• clarity
• emphasis
• a slightly more explicit mutual meaning

So these are all possible:

• Nous nous aidons.
• Nous aidons les uns les autres.
• Nous nous aidons les uns les autres.

The version in your sentence is a bit fuller and more emphatic. It makes the reciprocal meaning unmistakable.

Yes. That is grammatical and natural.

Compare:

• Nous nous aidons = we help each other
• Nous aidons les uns les autres = we help one another
• Nous nous aidons les uns les autres = we help each other, explicitly

So French has more than one way to express reciprocity here.

Because dans is the normal preposition for in / within a specific group.

• dans notre groupe = in our group

En is not used here with a possessed noun like notre groupe.

Be careful, though:

• en groupe means in groups or as a group

So:

• Nous travaillons en groupe = we work in groups / as a group
• Dans notre groupe = in our group, within our particular group

Because notre agrees with the noun groupe, and groupe is singular.

French possessive adjectives agree with the thing possessed, not with the number of owners.

So:

• notre groupe = our group
• nos groupes = our groups

Even though our refers to several people, the noun itself is singular, so French uses notre.

It can mean different things depending on context:

• the class
• the lesson
• the course
• sometimes even the material being studied

In this sentence, le cours devient difficile most naturally suggests that the class or lesson starts getting hard, or that the coursework becomes difficult.

French cours is a flexible school-related word, so the exact English choice depends on context.

Because the sentence is talking about one course, one class, or the lesson as a single whole.

French often uses the singular when referring to the specific class or subject currently being discussed.

If you wanted to talk about classes in general or several classes, you could say:

• quand les cours deviennent difficiles = when classes become difficult

But here the singular makes the situation feel more specific.

Because devient means becomes or starts to get.

So:

• le cours est difficile = the class is difficult
• le cours devient difficile = the class becomes difficult / starts getting difficult

Using devient shows a change. The lesson was not necessarily difficult at first, but then it gets harder.

Because the sentence describes a general habit or typical situation.

• nous nous aidons = we help each other
• quand le cours devient difficile = when the class becomes difficult

This is like saying what usually happens. French often uses the present tense this way, just like English:

• When it gets hard, we help each other.

If you were talking about a future situation, the tenses might change:

• Quand le cours deviendra difficile, nous nous aiderons.
• When the class becomes difficult, we will help each other.

Because aider normally takes a direct object in French.

You say:

• aider quelqu'un = to help someone

Not:

• aider à quelqu'un

So in nous nous aidons, the second nous is a direct-object pronoun.

This is useful to remember because some French verbs do need a preposition, but aider usually does not when followed by a person.

Yes. It can change for gender and sometimes structure.

In your sentence:

• les uns les autres is the normal masculine-plural form
• French also uses this form for a mixed group or when gender is unspecified

If the group were entirely feminine, you might see:

• les unes les autres

You may also see related forms with prepositions:

• les uns aux autres = to one another
• les uns avec les autres = with one another

The exact form depends on the verb and the grammar around it.

A helpful approximation is:

• noo noo-zay-don

More precisely, there is a liaison between the second nous and aidons:

• nous aidons sounds like nou-z-aidons

So:

• nous nous aidons is pronounced roughly noo noo-zay-don

The final sound in aidons is nasal, so it is not exactly like English don. But the key thing for learners is noticing the z sound linking nous to aidons.