الزملاء الذين يعرفون بأنفسهم ينضمون إلى الفريق.

The sentence is built like this:

• الزملاء = the colleagues
• الذين ... = who ...
• ينضمون إلى الفريق = join the team

So the full subject is really الزملاء الذين يعرفون/يعرّفون بأنفسهم — the colleagues who ... — and then the main predicate is ينضمون إلى الفريق.

A natural way to see it is:

• main noun: الزملاء
• relative clause describing that noun: الذين يعرفون/يعرّفون بأنفسهم
• main verb phrase: ينضمون إلى الفريق

The singular is زميل = colleague.

The plural زملاء is a broken plural, not a regular sound plural like -ون / -ين. Arabic has many plurals like this, where the inside of the word changes.

Because الزملاء refers to human males or a mixed group, Arabic uses masculine plural agreement with the verbs in the sentence.

الذين is the relative pronoun meaning who, whom, or that for a masculine plural human noun.

It matches الزملاء, which is plural and human.

Some matching forms are:

• الذي = who/that for masculine singular
• التي = who/that for feminine singular
• الذين = who/that for masculine plural human nouns

So الزملاء الذين ... means the colleagues who ...

Yes — but it depends on whether the noun is definite or indefinite.

Here, الزملاء is definite because it has الـ. After a definite noun, Arabic normally uses an explicit relative pronoun such as الذي / التي / الذين.

So:

• الزملاء الذين ... = the colleagues who ...

But with an indefinite noun, Arabic often does not use a relative pronoun:

• زملاء يعرّفون بأنفسهم ... = colleagues who introduce themselves ...

So الذين is here because الزملاء is definite.

This is a very good question, because normal Arabic writing often leaves out short vowels and shadda.

In plain text, يعرفون can be read as:

• يَعرِفون from عرف = they know
• يُعَرِّفون from عرّف = they introduce / identify

The context here strongly suggests يُعَرِّفون بأنفسهم = they introduce themselves.

Why?

Because عرّف بنفسه is a common expression meaning to introduce oneself.

If the meaning were truly know themselves, Arabic would more naturally say:

• يعرفون أنفسهم

without بـ.

So although the script shows يعرفون, the intended reading is very likely يعرّفون.

بأنفسهم breaks down into:

• بـ = with / by
• أنفس = selves
• هم = their / them

So together it means themselves in this expression.

In the phrase عرّف بنفسه, the preposition بـ is part of the idiom. So:

• عرّف بنفسه = he introduced himself
• عرّفوا بأنفسهم = they introduced themselves

This is not just a literal word-for-word translation from English; it is the normal Arabic pattern for this idea.

Because the subject is plural: الزملاء.

In Arabic, verbs agree with human plural subjects. Here you see the ending -ون, which marks 3rd person masculine plural in the indicative:

• يعرّفون = they introduce
• ينضمون = they join

Also, in this sentence the main subject comes before the main verb phrase, so full plural agreement is expected.

ينضمون comes from the verb انضمّ = to join.

Its dictionary form is:

• انضمّ إلى = to join / become part of

So the preposition إلى is the normal one used with this verb:

• انضمّ إلى الفريق = joined the team
• ينضمون إلى الفريق = they join / are joining the team

So إلى is not random here; it belongs to the verb.

Because ordinary Arabic script usually leaves out:

• short vowels
• many shaddas in everyday typing

So words can look less specific than they really are.

For example:

• يعرفون in plain text may actually be يُعَرِّفون
• ينضمون in plain text may actually be يَنضَمُّونَ

A more fully marked version would show those details, but most everyday Arabic does not.

This means learners often have to use context to decide which form is intended.

Yes. Arabic allows different word orders.

Your sentence starts with the noun phrase:

• الزملاء الذين ... ينضمون إلى الفريق

Arabic could also use a verb-first structure, such as:

• ينضمّ الزملاء الذين يعرّفون بأنفسهم إلى الفريق

In standard Arabic, when the verb comes first and the subject is an explicit plural noun after it, the verb is often singular in form:

• ينضمّ الزملاء
  not necessarily ينضمون الزملاء

So the given sentence uses a subject-first pattern, while a verb-first version is also possible.

The main things are:

• الذين should be read as one relative-pronoun unit
• يعرّفون needs a shadda if that is the intended meaning
• ينضمون also comes from a verb with a doubled consonant in the base form انضمّ
• إلى الفريق should be read smoothly as one prepositional phrase

A careful reading would sound roughly like:

• الزملاء الذين يُعَرِّفون بأنفسهم يَنضَمُّون إلى الفريق

The biggest pronunciation point is that the written form may hide a shadda that is understood from context.