Se vocês se ajudarem uns aos outros, vão acabar por concordar mais depressa.

They are two different ses:

• The first se means if.
• The second se is a pronoun linked to ajudarem and here gives a reciprocal sense: help each other.

So the structure is basically:

• Se = if
• vocês se ajudarem = you help each other

With a plural subject, se often has this reciprocal meaning.

Here, ajudarem is the future subjunctive of ajudar for vocês/eles/elas.

Portuguese uses the future subjunctive very often after se when talking about a future possibility or condition:

• Se vocês se ajudarem... = if you help each other...

This is one of the forms English speakers often find unusual because English does not really have an equivalent everyday tense.

Also, with regular verbs, the future subjunctive often looks exactly like the personal infinitive, so the form can be confusing. In this sentence, though, its job is future subjunctive.

In modern Portuguese, vocês takes third-person plural verb forms.

So you get:

• vocês vão
• vocês ajudam
• vocês concordam

This is normal, both grammatically and in everyday usage. Even though vocês means you (plural), the verb behaves like they grammatically.

Because Portuguese normally puts object pronouns before the verb in certain environments, and a clause introduced by se meaning if is one of those environments.

So standard Portuguese uses:

• Se vocês se ajudarem...

not:

• Se vocês ajudarem-se...

This is a rule of pronoun placement. In this kind of subordinate clause, proclisis is expected, meaning the pronoun comes before the verb.

Uns aos outros means to one another / each other.

In this sentence, it reinforces the reciprocal meaning already suggested by se:

• se ajudarem = help each other
• se ajudarem uns aos outros = help one another / help each other

So it is not strictly necessary, but it makes the meaning more explicit and often sounds very natural.

A useful extra detail:

• for a mixed group or a group of males: uns aos outros
• for an all-female group: umas às outras

This is made of two very common patterns:

1. ir + infinitive

   • vão acabar = are going to end up

2. acabar por + infinitive

   • acabar por concordar = end up agreeing / eventually come to agree

So the whole thing means something like:

• you are going to end up agreeing

It sounds more natural in Portuguese than translating each piece literally word for word.

Acabar por + infinitive means to end up doing something, to eventually do something, or to come to do something after a process.

So:

• vão acabar por concordar = they/you will end up agreeing

It suggests that agreement may not happen immediately, but it will be the final result.

Yes, you could say:

• Se vocês se ajudarem uns aos outros, concordarão mais depressa.

That is grammatically correct.

But the original sentence sounds more conversational and adds a nuance of eventually/end up:

• concordarão = you will agree
• vão acabar por concordar = you will end up agreeing

Also, in everyday spoken Portuguese, ir + infinitive is often more common than the simple future.

Depressa is a very common adverb meaning quickly.

So:

• mais depressa = more quickly / faster / sooner

It is very natural in European Portuguese.

Other possibilities exist:

• mais rapidamente = more formally more quickly
• mais rápido = common in speech, but some speakers prefer depressa when modifying a verb

So mais depressa is a very idiomatic choice here.

Vocês is the normal everyday plural you in most of Portugal.

Vós does exist, but it is usually:

• old-fashioned,
• regional,
• religious/liturgical,
• or stylistically marked.

So for ordinary modern European Portuguese, vocês is the form you should expect to hear and use most often.

Because that would normally change the meaning.

• Se vocês se ajudarem... uses the future subjunctive and refers to a future condition:
  If you help each other...

• Se vocês se ajudam... uses the present indicative and sounds more like a general or habitual idea:
  If/when you help each other (in general)...

So in this sentence, since the result is also in the future, ajudarem is the expected form.