Vi har känt våra nya grannar sedan vi flyttade in, och de har redan hjälpt oss två gånger.

Because they do different jobs in the sentence.

• har känt is the present perfect: har
  • känt. It shows a situation that started in the past and still matters now. In this sentence, the idea is that we started knowing the neighbors in the past, and we still know them now.
• flyttade is the simple past. It refers to a completed event at a specific point in the past: we moved in.

So the pattern is:

• ongoing situation up to now: Vi har känt ...
• the past event that marks the starting point: sedan vi flyttade in

That is very natural Swedish.

Swedish splits English know into different verbs.

• känna = to know a person, place, or thing through familiarity
• veta = to know a fact or piece of information

So:

• Jag känner Anna = I know Anna
• Jag vet svaret = I know the answer

In your sentence, känt våra nya grannar means known our new neighbors, so känna is the correct verb.

Känt is the form of känna used after har. In Swedish grammar, this is called the supine.

So:

• infinitive: känna
• present: känner
• past: kände
• supine: känt

You use the supine after har to make the present perfect:

• har känt
• har hjälpt

A useful shortcut is: if you see har + verb form, that second form is usually the supine.

Because grannar is plural.

• vår = our, for singular common-gender nouns
• vårt = our, for singular neuter nouns
• våra = our, for plural nouns

Since grannar means neighbors and is plural, Swedish uses våra.

Also, the adjective nya is plural too, matching the noun:

• vår nya granne = our new neighbor
• våra nya grannar = our new neighbors

Because the possessive already makes the noun definite.

In Swedish, if you use a possessive like min, din, vår, era, deras, you normally do not add a separate article.

So you say:

• våra nya grannar = our new neighbors

not

• de våra nya grannarna

The possessive already does the job of making the phrase specific.

Flytta in is a particle verb, similar to an English phrasal verb.

• flytta = move
• flytta in = move in

In Swedish, the particle often stays separate when the verb is conjugated:

• infinitive: att flytta in
• past: vi flyttade in

So sedan vi flyttade in means since we moved in.

This separation is normal:

• Jag kom in
• Hon gick ut
• Vi flyttade in

Because redan is a sentence adverb, and in Swedish these usually come after the finite verb.

Here, the finite verb is har, so the normal order is:

• de har redan hjälpt oss

not

• de redan har hjälpt oss

A very common Swedish pattern is:

• subject + finite verb + sentence adverb + main verb

For example:

• Jag har aldrig sett det
• Hon är redan hemma
• De har redan hjälpt oss

Because och does not trigger inversion.

In Swedish main clauses, the finite verb is usually in second position, but after a simple coordinating conjunction like och, the next clause starts normally with the subject:

• ..., och de har redan hjälpt oss ...

So the order is:

• de = subject
• har = finite verb
• redan = adverb
• hjälpt = main verb form
• oss = object

This is the standard main-clause word order.

Yes. Två gånger means two times or twice.

• en gång = once / one time
• två gånger = twice / two times
• tre gånger = three times

So de har redan hjälpt oss två gånger means they have already helped us twice.

In careful writing, it is spelled de, but in everyday speech it is very often pronounced dom.

So in natural spoken Swedish, many people would say something close to:

• dom har redan hjälpt oss två gånger

This is very common. The spelling stays de in standard writing, but the everyday pronunciation is usually dom.