Síðan við fluttum hingað þekkjum við fleiri íbúa í húsinu, og eldri íbúi á hæðinni fyrir ofan okkur gengur niður stigaganginn á hverjum morgni.

Here síðan means since. It introduces the time when the situation started:

• Síðan við fluttum hingað = Since we moved here

In other contexts, síðan can also mean then, after that, or later, so you have to use the context to decide which meaning it has.

This is normal Icelandic V2 word order.

When something other than the subject comes first in the sentence, the finite verb usually comes next. Here the whole clause Síðan við fluttum hingað comes first, so the main verb þekkjum comes before the subject við.

So the structure is:

• Síðan við fluttum hingað = first element
• þekkjum = finite verb
• við = subject

If the sentence began directly with the subject, you would get:

• Við þekkjum fleiri íbúa í húsinu.

Fluttum is the 1st person plural past tense of flytja, so:

• við fluttum = we moved

Hingað means to here / herewards and shows movement toward this place.

Compare:

• hér = here in a static sense
• hingað = to here

So við fluttum hingað means we moved here.

Because the two verbs describe different times:

• fluttum refers to the completed event of moving here
• þekkjum refers to the present situation now

So the sentence means that the move happened in the past, and as a result, the present state is that we know more residents now. English often uses something like Since we moved here, we’ve gotten to know more residents, but Icelandic can express the current state simply with the present tense here.

Þekkja is used for knowing people, places, or things through familiarity or acquaintance.

• Ég þekki hann = I know him
• Ég þekki þessa borg = I know this city

Vita is used for knowing facts or information:

• Ég veit það = I know that
• Veistu svarið? = Do you know the answer?

So þekkjum við fleiri íbúa means we know more residents in the sense of being acquainted with them.

Use fleiri with countable things, and meiri with amount or quantity.

• fleiri íbúar = more residents
• meira vatn = more water

Since residents are countable people, fleiri is the right word.

As for íbúa, it is the accusative plural form of íbúi because it is the direct object of þekkja.

Useful forms:

• íbúi = resident
• íbúar = residents, nominative plural
• íbúa = residents, accusative plural

Húsinu means the house / the building. Icelandic usually adds the definite article to the end of the noun.

Compare:

• hús = house / a house
• húsið = the house
• í húsinu = in the house / in the building

Also, when í means location rather than motion, it takes the dative case, which is why the form is húsinu.

Eldri íbúi means an older resident.

The adjective eldri is the comparative of gamall. This is an irregular pattern, so it does not look like a simple built form from gamall.

The main forms are:

• gamall = old
• eldri = older
• elstur = oldest

So yes, eldri is the correct comparative here. It means older, not necessarily elderly.

It means on the floor above us.

Breakdown:

• á hæðinni = on the floor / storey
• fyrir ofan okkur = above us

So the whole phrase describes where that resident lives: on the floor above ours.

Also, hæðinni is dative singular with the suffixed definite article, because á with location takes the dative here.

Because after a preposition, Icelandic normally uses an oblique case, not the nominative.

Compare:

• við = we
• okkur = us

So:

• fyrir ofan okkur = above us

For við, the accusative and dative form is both okkur, so you do not see a difference between those two cases here, but you definitely cannot use nominative við after the preposition.

Literally it means walks/goes down the stairwell or down the staircase.

Breakdown:

• gengur = walks / goes on foot
• niður = down
• stigaganginn = the stairwell / staircase

Stigaganginn is the definite accusative singular of stigagangur.

Compare:

• stigagangur = stairwell, stairway
• stigaganginn = the stairwell

English might translate this naturally as comes down the stairs every morning depending on context.

This is a common Icelandic time expression.

• á hverjum morgni literally = on every morning
• natural English = every morning

Hverjum is the dative singular form of hver, matching morgni, because á in this kind of repeated-time expression takes the dative.

So:

• á hverjum morgni = every morning