Hennes solglasögon låg i väskan bredvid nycklarna och mobilen.

Swedish uses sin/sitt/sina only when the possessor is the same as the subject of the clause.

In this sentence, the subject is solglasögon (sunglasses), not the woman they belong to. So sin/sina cannot be used here. You need hennes (her).

• Hennes solglasögon låg i väskan. = Her sunglasses were in the bag.
• Hon lade sina solglasögon i väskan. = She put her sunglasses in the bag.

In the second example, hon is the subject, and the sunglasses belong to her, so sina is correct there.

After a possessive like min, din, hans, hennes, vår, Swedish normally uses the noun in the indefinite form, even though the meaning is definite in English.

So Swedish says:

• hennes solglasögon = her sunglasses
  not
• hennes solglasögonen

This is a very common pattern:

• min bok = my book
• deras bil = their car
• hennes nycklar = her keys

So the possessive already makes the noun specific enough.

It is grammatically plural.

Solglasögon is one of those Swedish nouns that are normally used in the plural, just like English sunglasses. One pair of sunglasses is still usually called solglasögon.

So you can think of it like this:

• ett par solglasögon = a pair of sunglasses
• mina solglasögon = my sunglasses
• solglasögonen = the sunglasses

This is why it may look strange if you expect a singular word like sunglass, which English also normally does not use.

Låg is the past tense of ligga, which means to lie or to be lying.

Swedish often prefers a positional verb like:

• ligga = lie
• stå = stand
• sitta = sit

So instead of just saying something was somewhere, Swedish often says how it was positioned.

Here, solglasögon are understood as lying in the bag, so:

• solglasögon låg i väskan = the sunglasses were lying in the bag

In natural English, you might simply say were in the bag, but Swedish often uses låg in this kind of sentence.

Because Swedish verbs do not change form for singular and plural subjects.

So the same past-tense form is used whether the subject is one thing or many things:

• Boken låg på bordet. = The book was lying on the table.
• Böckerna låg på bordet. = The books were lying on the table.

So låg works fine with solglasögon, even though that noun is plural.

I means in/inside.

Since the sunglasses were inside the bag, i is the natural preposition:

• i väskan = in the bag

If you said på väskan, that would usually mean on the bag or on top of the bag, which is a different idea.

It is the definite ending.

Swedish usually puts the at the end of the noun instead of using a separate word before it.

• väska = a bag
• väskan = the bag

So i väskan literally means in the-bag, but in normal English we simply say in the bag.

The same thing happens elsewhere in the sentence:

• nycklarna = the keys
• mobilen = the phone

They are definite because the sentence is referring to specific things: the keys and the phone, not just any keys or any phone.

Their forms are:

• nyckel = a key
• nycklar = keys
• nycklarna = the keys

and

• mobil = a mobile phone
• mobilen = the mobile phone

So bredvid nycklarna och mobilen means next to the keys and the phone.

Because nycklarna is plural definite, while mobilen is singular definite.

• nycklarna = the keys
• mobilen = the phone

So the sentence is talking about more than one key, but only one phone.

This is just normal noun agreement, not anything unusual about the sentence structure.

Bredvid means next to or beside.

It is followed directly by the thing something is next to:

• bredvid stolen = next to the chair
• bredvid huset = beside the house

So:

• bredvid nycklarna och mobilen = next to the keys and the phone

Here, och simply joins the two nouns, so the sunglasses were next to both of those things.

Yes. Swedish often allows different word order depending on what you want to emphasize.

The original sentence starts with the subject:

• Hennes solglasögon låg i väskan bredvid nycklarna och mobilen.

But you could also start with the place:

• I väskan låg hennes solglasögon bredvid nycklarna och mobilen.

That sounds natural too. Notice that when a different element comes first in a main clause, Swedish keeps the verb in the second position, so låg comes before hennes solglasögon.

This is the usual Swedish V2 word order pattern.