Náttfötin hennar eru blá, en inniskórnir eru hvítir.

Yes. Náttföt means pajamas / nightclothes and is normally used as a plural noun in Icelandic, much like pajamas in English.

So:

• náttföt = pajamas
• náttfötin = the pajamas

Because it is plural, it also takes the plural verb eru.

In Icelandic, the definite article is usually attached to the end of the noun instead of written as a separate word.

In this sentence:

• náttfötin = náttföt
  • definite ending = the pajamas
• inniskórnir = inniskór
  • definite ending = the slippers

So Icelandic often builds the directly into the noun.

Hennar means her, and here it is a genitive pronoun used to show possession.

A very common Icelandic pattern is:

• definite noun + possessor

So:

• náttfötin hennar = her pajamas
• literally something like the pajamas of hers

This sounds normal and natural in Icelandic.

That is just a normal Icelandic possession pattern. When Icelandic uses a noun plus a following possessor like hennar, the noun is often definite.

So Icelandic prefers:

• náttfötin hennar

rather than trying to match English structure exactly.

Even though it may look like the pajamas her word-for-word, it simply means her pajamas.

Eru is the present plural form of vera (to be).

Both subjects are plural:

• náttfötin = plural
• inniskórnir = plural

So Icelandic uses:

• eru blá
• eru hvítir

If the subject were singular, you would use er instead.

Because they are not being used directly before the noun as ordinary modifiers. They are predicate adjectives after the verb vera (to be).

Compare:

• blá náttföt = blue pajamas
• náttfötin eru blá = the pajamas are blue

And:

• hvítir inniskór = white slippers
• inniskórnir eru hvítir = the slippers are white

So after are, Icelandic places the color adjective after the verb, just as English does.

Because Icelandic adjectives must agree with the noun they describe in gender and number.

Here:

• náttfötin is neuter plural, so the adjective is blá
• inniskórnir is masculine plural, so the adjective is hvítir

So the different endings show grammatical agreement, not a difference in meaning.

That ending shows that the noun is masculine plural definite in the nominative.

So:

• inniskór = slippers
• inniskórnir = the slippers

This is different from náttfötin, which is a neuter plural noun and therefore has a different definite ending.

Grammatically, hennar belongs only to náttfötin in this sentence.

So the sentence explicitly says:

• her pajamas
• but just the slippers

If you wanted to say her slippers too, you would normally say:

• inniskórnir hennar

Whether the slippers are also hers can sometimes be understood from context, but the wording itself attaches hennar only to the first noun.

Here, en means but.

It links the two parts of the sentence:

• Náttfötin hennar eru blá
• en inniskórnir eru hvítir

So it contrasts the two descriptions: blue pajamas, but white slippers.

A useful extra note: in other contexts, en can also mean than, but in this sentence it clearly means but.