אלה האנשים שראינו אתמול.

Because in Hebrew, the verb to be is usually not stated in the present tense.

So:

• אלה האנשים = These are the people
• literally, it is more like These the-people

This is completely normal Hebrew.
In the past or future, Hebrew does use forms of to be:

• אלה היו האנשים = These were the people
• אלה יהיו האנשים = These will be the people

But in the present, the copula is usually omitted.

אלה means these.

It is a plural demonstrative. In modern Hebrew, אלה is commonly used for plural nouns, whether they are masculine or feminine.

Examples:

• אלה האנשים = these people
• אלה הנשים = these women

So in this sentence, אלה points to a specific group: these people.

The prefix ה־ is the Hebrew definite article, meaning the.

So:

• אנשים = people / men
• האנשים = the people

Since the sentence means These are the people we saw yesterday, the noun is definite in English and in Hebrew, so ה־ is needed.

That is because אנשים is an irregular plural.

The singular is:

• איש = man / person

The plural is:

• אנשים = people / men

This is just something you need to learn as a vocabulary item. Hebrew has quite a few common irregular plurals.

שראינו is made of two parts:

• ש־ = that / who / which
• ראינו = we saw

So:

• שראינו = that we saw / who we saw

Breaking down ראינו further:

• root: ר־א־ה = related to seeing
• ראינו = we saw

The ending ־נו means we in the past tense.

ש־ is a very common Hebrew relative particle. It introduces a clause like that, who, or which in English.

So:

• האנשים שראינו = the people that we saw
• more naturally in English: the people we saw

It connects האנשים to the extra information ראינו אתמול.

In more formal Hebrew, you may also see אשר, but ש־ is much more common in everyday language.

Because Hebrew does not need to repeat the object in this kind of relative clause.

In English, we say:

• the people we saw

We do not say:

• the people we saw them ❌

Hebrew works similarly here:

• האנשים שראינו = the people we saw

So the object is understood to be the people, and it does not need to appear again inside the relative clause.

For the same reason: the object is not explicitly repeated inside the relative clause.

Normally, if you say we saw the people, you would say:

• ראינו את האנשים

Here, though, the people is already the noun being described:

• האנשים שראינו אתמול

That means literally the people that we saw yesterday, where the object position is left empty because it refers back to האנשים.

So you do not say:

• האנשים שראינו את ... ❌

because there is no explicit object after את.

אתמול means yesterday.

In this sentence:

• ראינו אתמול = we saw yesterday

Putting אתמול at the end is very natural. Hebrew word order is somewhat flexible, but this order is common and neutral.

You could sometimes move time expressions for emphasis, but the basic version here is perfectly standard:

• אלה האנשים שראינו אתמול.

In modern Hebrew, אלה is generally used as the plural these for both masculine and feminine nouns.

So you can say:

• אלה האנשים = these people (masculine noun)
• אלה הנשים = these women (feminine noun)

So here, even though האנשים is masculine plural, אלה is exactly what you would expect.

Yes. אלו is also used and means the same thing here: these.

So both of these are possible:

• אלה האנשים שראינו אתמול
• אלו האנשים שראינו אתמול

In modern usage, אלה is extremely common.
אלו can sound a bit more formal or stylistic to some speakers, but both are normal forms you may encounter.

Sometimes, yes, depending on context.

Hebrew demonstratives do not always map perfectly onto English this/that and these/those in every situation. אלה most directly means these, but in real conversation it can sometimes be translated more naturally as those, especially if English would prefer that in the situation.

Still, if you are learning the basic meaning, אלה = these is the safest starting point.

The sentence has two main parts:

1. אלה האנשים = These are the people
2. שראינו אתמול = that we saw yesterday

So the full structure is:

• [These] [the people] [that we saw yesterday]

A useful way to think of it is:

• אלה = points to the group
• האנשים = names the group
• שראינו אתמול = describes which people you mean

That is why the sentence feels very compact in Hebrew, even though it is perfectly natural.