Í janúar og febrúar er oft kaldast, svo við erum meira heima.

Because Icelandic main clauses usually follow the verb-second pattern. If you start the sentence with a time phrase like Í janúar og febrúar, the finite verb normally comes next:

• Í janúar og febrúar er ...

This is very common in Icelandic. English can do something similar, but Icelandic is more systematic about it.

This is an impersonal sentence, like a weather statement. Icelandic often does not need an expressed dummy subject here.

A fuller idea behind the sentence is something like:

• Það er oft kaldast í janúar og febrúar.

But when the sentence begins with a time phrase, Icelandic very naturally says:

• Í janúar og febrúar er oft kaldast.

So English needs it, but Icelandic often does not.

Kaldast is the superlative form of kaldur (cold).

The basic comparison is:

• kalt = cold
• kaldara = colder
• kaldast = coldest

In weather-style expressions, Icelandic usually uses the neuter singular form:

• Það er kalt. = It is cold.
• Það er kaldara. = It is colder.
• Það er kaldast. = It is coldest.

So here kaldast means coldest, not just very cold.

Because janúar og febrúar are not the grammatical subject of the sentence. They are just telling you when something is true.

The sentence does not mean:

• January and February are often the coldest as a plural subject in the grammar of the clause.

Instead, it means something more like:

• During January and February, it is often coldest.

So the verb stays in the usual singular impersonal form: er.

Oft means often, and its position is normal in Icelandic.

In this sentence:

• Í janúar og febrúar er oft kaldast

the order is:

1. time phrase
2. finite verb
3. adverb (oft)
4. complement (kaldast)

That is a very natural word order. You may see adverbs move around in Icelandic for emphasis, but this placement is neutral and common.

Here svo means so, therefore, or as a result.

It connects the first part and the second part as cause/result:

• It is often coldest in January and February, so we stay home more.

So in this sentence, svo is not the so of so big or so that. It is the result word.

Because meira is being used adverbially, not as an adjective agreeing with a noun.

Here it means more in the sense of to a greater extent:

• við erum meira heima = we are at home more

Compare:

• meiri = adjective form, used with nouns
• meira = adverbial/neuter form, often used for more

So this sentence is not describing a noun as bigger/greater. It is describing how much they are at home.

No. Heima is an adverb, meaning at home.

So:

• vera heima = to be at home

This is a very common Icelandic pattern. You do not need a preposition here.

It is useful to compare:

• heima = at home, at one's home
• heim = homeward, to home

So:

• Ég er heima. = I am at home.
• Ég fer heim. = I am going home.

In your sentence, heima is correct because the meaning is location, not movement.

Because the idea is more at home than usual / more than at other times, not the most at home in an absolute sense.

• meira = more
• mest = most

So:

• við erum meira heima = we are at home more
• við erum mest heima would mean something more like we are at home the most

The sentence is making a simple comparison with other times of year, so meira is the natural choice.

Í is the normal preposition used with months in expressions like in January and in February.

So you learn:

• í janúar = in January
• í febrúar = in February

Also, month names in Icelandic usually appear without an article, just like in English:

• í janúar, not í the January

A learner may expect a visible case ending after í, but with janúar and febrúar, the form does not visibly change here, so the phrase looks simple on the surface.

Not necessarily. The present tense in Icelandic is often used for general truths, habits, and regular patterns.

So this sentence means something like:

• In January and February it is often coldest, so we tend to stay home more.

It is a general statement about what usually happens, not only about this exact moment.

Yes, that is possible and understandable. But Í janúar og febrúar er oft kaldast is very natural because it puts the time frame first.

The version in your sentence feels a bit like:

• As for January and February, that is when it is often coldest.

So the chosen word order is especially good when the speaker wants to highlight the time period first.