На собеседование кандидаты заходили поодиночке.

In Russian, на is often used with events, appointments, and activities:

• на собеседование = to an interview
• на встречу = to a meeting
• на урок = to a lesson
• на концерт = to a concert

So на собеседование means to the interview in the sense of going there to take part in it.

By contrast, в is more typical for going into a physical enclosed space:

• в комнату = into the room
• в офис = into the office

Russian treats собеседование more like an event than like a container, so на is the normal choice.

It is accusative singular.

Why? Because на can take different cases, and here it expresses direction toward a destination, so it takes the accusative:

• идти на собеседование = to go to an interview
• прийти на собеседование = to arrive for an interview

Since собеседование is a neuter inanimate noun, its nominative and accusative forms look the same:

• nominative: собеседование
• accusative: собеседование

Because кандидаты is the subject of the sentence: the candidates are the ones doing the action.

The dictionary form is кандидат. In the plural nominative, it becomes:

• кандидат → кандидаты

So the structure is:

• кандидаты заходили = the candidates were going in / entered

Here заходили means something like went in or entered.

It comes from the verb заходить, which can have several meanings in different contexts, but in this sentence it clearly means to go in / to step in.

Compare:

• входить = to enter, to go in
• заходить = to go in, to step in, often with a sense of crossing into a place

In this sentence, заходили suggests the candidates were going into the room or office where the interview was happening.

This is a very common question.

Even though each candidate entered only once, the sentence looks at the situation as a process or repeated sequence:

• one candidate went in
• then another
• then another

So Russian uses the imperfective заходили to present this as an ongoing or repeated action in the past.

Зашли would sound more like a simple completed fact:

• На собеседование кандидаты зашли поодиночке.

This is possible, but заходили paints the scene more naturally as they were going in one by one.

Because the subject is plural.

In the past tense, Russian verbs agree with the subject in gender and number:

• masculine singular: заходил
• feminine singular: заходила
• neuter singular: заходило
• plural: заходили

Since кандидаты is plural, the verb must be заходили.

Поодиночке is an adverb meaning:

• one by one
• individually
• singly
• not together

So the sentence means the candidates did not go in as a group. They entered separately, one at a time.

This word is often used when people act separately rather than collectively.

They are very close, and in many contexts both can be translated as one by one.

A useful distinction is:

• поодиночке = individually, separately, not together
• по одному = one at a time, one each, in single units

In this sentence, поодиночке emphasizes that the candidates went in separately rather than as a group.

If you said по одному, it would sound a bit more like counting them off one at a time.
Both are possible, but поодиночке feels especially natural here.

Yes, it is natural.

Russian word order is flexible, and the beginning of the sentence often sets the scene or highlights what the speaker wants to frame first.

Starting with На собеседование does this:

• it establishes the situation first: as for the interview
• then it tells you who did the action: кандидаты
• then how: поодиночке

A more straightforward order is also possible:

• Кандидаты заходили на собеседование поодиночке.

That version is also correct. The original just sounds a little more scene-setting.

Not only, but that is one of its most common meanings.

Собеседование can refer to:

• a job interview
• an interview-style meeting
• sometimes an oral evaluation or conversation in educational or official contexts

So in many everyday situations, especially with кандидаты, learners will correctly understand it as a job interview.

Yes, in many contexts came in works well in English.

Whether English uses came in or went in depends on point of view:

• came in if you imagine the speaker located inside the room
• went in if you are describing the action more neutrally from outside

Russian заходили itself does not force that exact English distinction. It simply expresses the entering action.