Deras hus ligger nära sjön.

In Swedish, a possessive word like min, din, hans, hennes, deras usually replaces the article.

So:

• huset = the house
• deras hus = their house

You normally do not combine a possessive with the usual definite ending in this kind of phrase.

So deras hus is the normal way to say their house.

A useful pattern is:

• ett hus = a house
• huset = the house
• deras hus = their house

Because Swedish possessives do not make the noun change in the same way English sometimes does with apostrophes or other structures. The noun usually stays in its basic form after a possessive.

So:

• deras hus = their house
• min bil = my car
• hans bok = his book

Also, hus is an ett-word, but after a possessive you still just say hus, not ett hus.

Deras means their.

Unlike English, where you have different forms like his, her, their, Swedish has:

• hans = his
• hennes = her
• deras = their

Deras does not change depending on the gender or number of the thing owned. It stays deras whether it is one thing or several:

• deras hus = their house
• deras bilar = their cars

Swedish often prefers a position verb when talking about where something is located.

Here, ligger is from ligga, which literally means lie or be lying, but it is also very commonly used to mean that something is located somewhere.

So:

• Huset ligger nära sjön = the house is located near the lake

Swedish uses these position/location verbs more than English does:

• ligga = lie / be located
• stå = stand
• sitta = sit

For buildings, places, towns, islands, and many objects, ligga is very common.

Using är would often sound less natural here.

Ligger is the present tense of ligga.

The forms are:

• att ligga = to lie / to be located
• ligger = lies / is lying / is located
• låg = lay / was located
• legat = lain / been located

In this sentence, the subject is hus (house), and the sentence is talking about a present fact, so ligger is the correct form.

Because nära can work directly as a preposition in Swedish, meaning near.

So you say:

• nära sjön = near the lake
• nära huset = near the house

You do not need till here.

English speakers often want to add an extra preposition, but Swedish does not.

Compare:

• nära skolan = near the school
• långt från skolan = far from the school

Because sjön is the definite singular form of sjö.

• en sjö = a lake
• sjön = the lake

Many Swedish nouns add the definite article as an ending. For en-words ending in a vowel, that ending is often just -n.

So:

• sjö → sjön
• flicka → flickan
• ö → ön

This is one of the big differences from English: Swedish often puts the at the end of the noun.

This is the normal Swedish main-clause word order:

• subject
  • verb
    • other information

So here:

• Deras hus = subject
• ligger = verb
• nära sjön = place expression

This is very similar to basic English word order.

But Swedish also has the V2 rule in main clauses, meaning the finite verb must come in the second position. So if you begin with another element, the verb still stays second:

• Nära sjön ligger deras hus.

That is also correct, but the original sentence is the most straightforward version.

Yes, but not in this sentence.

Swedish uses sin/sitt/sina for a reflexive possessive, meaning the owner is the subject of the same clause.

Examples:

• De älskar sitt hus. = They love their own house.
  Here de are the subject, and the house belongs to them, so sitt is used.

But in:

• Deras hus ligger nära sjön.

the subject is deras hus, not de. So Swedish uses deras, not sina.

This is a very common learner issue:

• De säljer sitt hus. = They are selling their own house.
• De säljer deras hus. = They are selling someone else’s house, or their referring to another group.

Because sjö is an en-word, not an ett-word.

You have to learn the gender of each noun:

• ett hus → huset
• en sjö → sjön

So the definite form depends on whether the noun is an en-word or an ett-word.

Very roughly:

• en-word definite singular often ends in -en or -n
• ett-word definite singular often ends in -et or -t

Since sjö is en sjö, the definite form is sjön.

This is one of the trickiest sounds in Swedish.

A rough guide:

• sjön sounds approximately like hurn/shurn to an English speaker, but there is no exact English equivalent.
• The sj sound is a special Swedish sound made far back in the mouth.
• The ö vowel is also not exactly English. It is somewhat like the vowel in British bird for some speakers, but not identical.

So a rough learner-friendly pronunciation might be:

• sjön ≈ shurn / hwurn
  depending on accent and how precisely you are trying to imitate Swedish

The important thing is:

• it is not pronounced like English see-on
• it is one syllable

Yes, very common.

Swedish frequently uses:

• ligger i = is located in
• ligger på = is located on
• ligger nära = is near
• ligger långt från = is far from

Examples:

• Stockholm ligger i Sverige.
• Huset ligger på landet.
• Skolan ligger nära stationen.

So ligger nära sjön is a very natural Swedish way to describe location.