Við heimsækjum frænku okkar þegar við förum í frí.

Frænka is a feminine family term that covers several English words:

• aunt (father’s or mother’s sister, or aunt by marriage)
• niece
• female cousin

In this sentence, frænku could be our aunt, our niece, or our (female) cousin, and context would normally make it clear which one is meant.

Frænka is a feminine noun. Its singular forms are:

• Nominative: frænka (subject)
• Accusative: frænku (direct object)
• Dative: frænku
• Genitive: frænku

In the sentence, frænku is the direct object of the verb heimsækjum (we visit), so it must be in the accusative case, hence frænku, not frænka.

Icelandic usually puts possessive pronouns after the noun:

• frænka okkar – our aunt
• bílinn minn – my car
• húsið þeirra – their house

So frænku okkar is the normal word order: noun + possessive.
Putting the possessive before the noun is possible but has a special, emphatic feel (see next question).

Yes, okkar frænku is grammatically possible, but it is emphatic or contrastive.

• Við heimsækjum frænku okkar – neutral: We visit our aunt.
• Við heimsækjum okkar frænku – more like: We visit *our aunt (as opposed to someone else’s).*

Placing okkar first highlights the our part, often contrasting with someone else’s relative or stressing the belonging. In normal, non-contrastive speech, frænku okkar is preferred.

These are different case forms of the first-person plural:

• við – nominative, used for the subject:

  • Við heimsækjum frænku okkar. – We visit our aunt.

• okkur – accusative and dative, used for object / indirect object:

  • Hún heimsækir okkur. – She visits us.
  • Hann gaf okkur bók. – He gave us a book.

• okkar – genitive, often used as a possessive:

  • frænka okkar – our aunt
  • húsið okkar – our house

So in your sentence: við is the subject, okkar marks possession.

Heimsækja is the infinitive (to visit). It conjugates in the present tense like this:

• ég heimsæki – I visit
• þú heimsækir – you (sg.) visit
• hann / hún / það heimsækir – he / she / it visits
• við heimsækjum – we visit
• þið heimsækið – you (pl.) visit
• þeir / þær / þau heimsækja – they visit

Because the subject is við (we), you must use the first person plural form: heimsækjum.

Icelandic normally uses the present tense to talk about the future when the future event is planned, expected, or scheduled:

• Við förum á morgun. – We go / are going tomorrow.
• Ég kem seinna. – I will come later.

So Við heimsækjum frænku okkar þegar við förum í frí. naturally means
We’ll visit our aunt when we go on holiday., even though the verbs are in the present tense.

There is a future auxiliary verb munu (e.g. við munum heimsækja), but everyday speech uses the present for most future meanings.

Þegar means when (in the sense “at the time that”).

It introduces a subordinate clause:
þegar við förum í frí – when we go on holiday

Word order inside this clause stays subject–verb–other elements:

• þegar
  • við (subject) + förum (verb) + í frí (rest)

Unlike in English questions (e.g. When do we go?), Icelandic does not invert the subject and verb here. You do not say þegar förum við í frí in this meaning; that would sound wrong in this context.

No. In Icelandic, subject pronouns are not usually dropped, and the verb must agree with an explicit subject unless there is some other special construction.

So you need:

• þegar við förum í frí – when we go on holiday

Leaving out við (when go on holiday) is ungrammatical in standard Icelandic.

The verb fara (to go) commonly combines with the preposition í plus a noun to express going into / entering a state or place:

• fara í skólann – go to school
• fara í vinnu – go to work
• fara í frí – go on holiday

Til usually means to / towards a person or place (direction), not a state:

• fara til Íslands – go to Iceland
• fara til læknis – go to the doctor

Since frí here is “holiday, time off” (a state), the standard phrase is fara í frí.

Frí (holiday, time off) has the following singular forms:

• Nominative: frí
• Accusative: frí
• Dative: fríi
• Genitive: frís

The preposition í can take accusative or dative:

• í
  • accusative → movement into: into, to, onto
• í
  • dative → location in: in, at

So:

• fara í frí – go on holiday (movement → accusative frí)
• vera í fríi – be on holiday (state/location → dative fríi)

In your sentence, förum í frí uses the accusative because you are going into the holiday.

Approximate pronunciation (IPA):

• heimsækjum: [ˈheimsai̯cʏm]

  • hei as in English hey
  • ms pronounced together, æ here written as æ in the infinitive (heimsækja) but umlaut gives heimsækjum with æ → ai̯ sound
  • kj is a voiceless palatal stop/fricative, something like a softer ky
  • u here is [ʏ], similar to German ü in Mütter

• frænku: [ˈfrai̯ŋkʏ]

  • fræ is [frai̯], like fry but with an [a] start
  • nk is pronounced [ŋk], like nk in bank
  • final u again [ʏ]

Stress is on the first syllable: HEIM-sæk-jum, FRÆN-ku.

You could say:

• Við förum til frænku okkar þegar við förum í frí.

This means We go to our aunt when we go on holiday. It focuses on the going to (her place) rather than the act of visiting itself.

Heimsækja specifically means to visit (someone/something).
Fara til frænku okkar literally means go to our aunt; it strongly implies visiting, but uses a more general motion verb.

Both can be natural, but heimsækja is the straightforward word for to visit.