Sur la sofo estas du molaj kusenoj, kaj ni lasas la katon dormi inter ili.

This is a very common Esperanto pattern for introducing the existence of something somewhere:

Sur la sofo estas du molaj kusenoj.
= On the sofa are two soft cushions / There are two soft cushions on the sofa.

In Esperanto, when you want to say that something exists in a place, it is very natural to begin with the location and then use estas.

You could also say:

Du molaj kusenoj estas sur la sofo.

That is grammatical too, but Sur la sofo estas... sounds especially natural when you are presenting what is there.

Because sur means on, while en means in.

• sur la sofo = on the sofa
• en la sofo = in the sofa

A cushion normally rests on top of a sofa, not inside it, so sur is the right preposition here.

Because in Esperanto, adjectives must agree with the nouns they describe.

Here:

• kuseno = a cushion
• kusenoj = cushions
• mola = soft
• molaj = soft, plural

Since kusenoj is plural, the adjective mola also becomes plural:

• du molaj kusenoj = two soft cushions

This agreement is very regular in Esperanto:

• singular noun → singular adjective
• plural noun → plural adjective
• accusative noun → adjective also takes -n

La is the definite article, meaning the.

It is used when the speaker is talking about a specific thing:

• la sofo = the sofa
• la kato / la katon = the cat

But du molaj kusenoj already has du (two), and in Esperanto you normally do not combine la with a plain numeral in a phrase like this.

So:

• du molaj kusenoj = two soft cushions
• not usually la du molaj kusenoj unless you specifically mean the two cushions already known in context

In this sentence, the cushions are being introduced, so no la is needed.

Because la katon is the direct object of lasas.

The verb lasi means to let or to allow. In the sentence:

ni lasas la katon dormi

the thing being allowed is the cat, so kato takes the accusative ending -n:

• kato = cat
• katon = cat as a direct object

This is one of the most important Esperanto patterns: direct objects usually take -n.

Because after lasi, Esperanto normally uses an infinitive.

• lasi = to let
• dormi = to sleep

So:

ni lasas la katon dormi
literally = we let the cat sleep

If you used dormas, that would be a finite verb, and the structure would not work here.

Compare:

• La kato dormas. = The cat is sleeping.
• Ni lasas la katon dormi. = We let the cat sleep.

After verbs like lasi, vidi, aŭdi, and some others, Esperanto often uses this object + infinitive pattern.

It has this structure:

ni — subject
lasas — main verb
la katon — direct object of lasas
dormi — infinitive explaining what the cat is allowed to do

So it works like:

We let + the cat + sleep

This is very similar to English, except Esperanto marks the object clearly with -n.

A few similar examples:

• Mi vidas lin kuri. = I see him run/running.
• Ŝi aŭdas la infanon plori. = She hears the child cry/crying.
• Ili lasas nin eniri. = They let us enter.

Because inter here describes location, not direction toward a place.

• inter ili = between them

The cat is sleeping in a position between the cushions. That is simple location, so the pronoun stays without -n.

In Esperanto, after a preposition, you normally do not add -n unless you want to show direction or movement toward something.

Compare:

• La kato dormas inter ili. = The cat sleeps between them.
• La kato iras inter ilin. = The cat goes in between them.

So in this sentence, inter ili is correct because the cat is already located there.

Ili refers to du molaj kusenoj.

So:

• du molaj kusenoj = two soft cushions
• ili = they / them

After the preposition inter, English uses them, but Esperanto uses the same basic pronoun form ili after a preposition unless there is a reason to add -n.

Also notice that Esperanto pronouns do not change for grammatical gender in the plural:

• ili can mean they or them for people, animals, or things

Because Esperanto usually does not need a dummy subject like English there.

English says:

• There are two cushions on the sofa.

Esperanto simply says:

• Sur la sofo estas du kusenoj.

The verb esti works without an extra filler word. The sentence directly states that two cushions exist in that place.

So English there is/there are often corresponds simply to estas in Esperanto.

Yes, Esperanto word order is fairly flexible, because endings show the grammar clearly.

For example, these are all possible:

• Sur la sofo estas du molaj kusenoj.
• Du molaj kusenoj estas sur la sofo.

And in the second half:

• Ni lasas la katon dormi inter ili.
• Inter ili ni lasas la katon dormi.

However, the original version sounds very natural:

• first the place is introduced
• then the things on it
• then what is happening with the cat

So even though Esperanto allows flexibility, some orders sound more natural depending on what you want to emphasize.

Because Esperanto normally marks plural on the noun even when a number is present.

So:

• du kusenoj = two cushions
• not du kuseno

This may feel redundant to an English speaker, but it is standard Esperanto grammar. The plural marker -j is still used, and any adjective also agrees:

• du molaj kusenoj

This makes noun phrases very clear and regular.

Yes. Sofo is a normal Esperanto noun meaning sofa.

Like most Esperanto nouns, it ends in -o:

• sofo = sofa
• kato = cat
• kuseno = cushion

And it changes regularly:

• la sofo = the sofa
• sur la sofo = on the sofa

So this sentence is also a good example of how easy Esperanto nouns are to recognize.

Lasas is the present tense form of lasi.

Esperanto tense endings are very regular:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = imperative/jussive
• -i = infinitive

So:

• ni lasas = we let / we are letting
• ni lasis = we let / we allowed
• ni lasos = we will let

In this sentence, lasas matches the present-time situation being described.