אחד האנשים הכי אמיצים שאני מכירה הוא גם אחד האנשים הכי מנומסים במשרד.

Yes, literally it is one of the people / one of the men.

In Hebrew, אחד האנשים is a very common way to say one of the people or one of the men. You will also often hear:

• אחד מהאנשים = one of the people

Both are used. The version without מ־ is very common, especially in natural spoken and written Hebrew.

Also, אנשים technically means people, but in some contexts it can also mean men, depending on who is being talked about.

Because the structure is one of the most brave people, not simply the brave person.

Hebrew is describing the larger group:

• אחד האנשים הכי אמיצים = one of the bravest people

Since אנשים is plural, the adjective אמיצים is also plural.

The same thing happens later:

• אחד האנשים הכי מנומסים = one of the most polite people

So even though the sentence is ultimately about one individual, the adjective agrees with אנשים, which is plural.

Because מכירה shows that the speaker is female.

Hebrew verbs in the present tense agree with the subject in gender and number. So:

• אני מכיר = I know said by a male speaker
• אני מכירה = I know said by a female speaker

So this sentence is being said by a woman. If a man were saying it, it would be:

• אחד האנשים הכי אמיצים שאני מכיר...

שאני is made of:

• ש־ = that / who / which
• אני = I

So:

• שאני מכירה = that I know / whom I know

In this sentence, it introduces a relative clause:

• אחד האנשים הכי אמיצים שאני מכירה
  = one of the bravest people that I know

Because Hebrew uses different verbs for different kinds of know.

• להכיר = to know a person, be acquainted with, be familiar with
• לדעת = to know a fact, know information

So:

• אני מכירה אותו = I know him
• אני יודעת את התשובה = I know the answer

Since the sentence is about knowing a person, מכירה is the correct verb.

הכי means most and is a very common way to form the superlative in everyday Hebrew.

So:

• אמיץ = brave
• הכי אמיץ = most brave / bravest
• הכי אמיצים = most brave / bravest (plural)

In the sentence:

• הכי אמיצים = the bravest
• הכי מנומסים = the most polite

A very natural translation is:

• one of the bravest people
• one of the most polite people

Because in the common הכי + adjective structure, הכי already gives the superlative idea, so you normally say:

• הכי אמיץ
• הכי מנומס
• הכי אמיצים
• הכי מנומסים

You do not usually say הכי האמיצים here.

So:

• האנשים הכי אמיצים = the bravest people
• האנשים הכי מנומסים = the most polite people

This is the normal modern Hebrew pattern.

הוא means he is, and גם means also / too.

So:

• הוא גם אחד האנשים הכי מנומסים במשרד = he is also one of the most polite people in the office

The word גם connects the two qualities:

1. he is one of the bravest people
2. he is also one of the most polite people

Because Hebrew often attaches prepositions directly to the noun.

Here:

• ב־ = in
• המשרד = the office

When ב־ combines with ה־, they contract:

• ב + המשרד = במשרד

So במשרד means in the office or at the office.

For the same reason as אמיצים: it agrees with אנשים, which is plural masculine.

• אחד האנשים הכי מנומסים = one of the most polite people

Even though only one individual is being singled out, Hebrew is still using the plural group noun אנשים, so the adjective is plural too.

Because in Hebrew, adjectives normally come after the noun they describe.

For example:

• איש אמיץ = a brave man
• אנשים אמיצים = brave people
• אנשים מנומסים = polite people

So:

• האנשים הכי אמיצים
• האנשים הכי מנומסים

This is normal Hebrew word order.

Yes. A more formal or literary alternative is:

• אחד האנשים האמיצים ביותר שאני מכירה...
• אחד האנשים המנומסים ביותר במשרד...

That also means:

• one of the bravest people I know
• one of the most polite people in the office

But in everyday modern Hebrew, הכי is usually more common and natural.

The dictionary-style masculine singular forms are:

• אמיץ = brave
• מנומס = polite

Their plural masculine forms are:

• אמיצים
• מנומסים

Their feminine singular forms would be:

• אמיצה
• מנומסת

And feminine plural:

• אמיצות
• מנומסות

Not always. אנשים literally means people, and it is grammatically masculine plural.

In real usage, it can refer to:

• a group of men
• a mixed group
• people in general

Sometimes, depending on context, English may translate it as men, but very often people is the better translation.

That is close to the literal structure, but it sounds unnatural in English.

A smoother English translation is:

• One of the bravest people I know

Hebrew often uses structures that map a little differently onto English, so it is better to understand the pattern as a whole rather than word-for-word.