Ne možemo još ostati ovdje.

Croatian often drops subject pronouns because the verb ending already tells you who the subject is.

Here, možemo ends in -mo, which shows 1st person plural: we.

So:

• Ne možemo još ostati ovdje. = normal, natural Croatian
• Mi ne možemo još ostati ovdje. = also possible, but mi adds emphasis, contrast, or emotion

For example:

• Mi ne možemo još ostati ovdje, ali vi možete.
  We can't stay here any longer, but you can.

Možemo is the present tense, 1st person plural form of the verb moći, which means can / to be able to.

So:

• mogu = I can
• možeš = you can
• može = he/she/it can
• možemo = we can
• možete = you (plural/formal) can
• mogu = they can

In this sentence, ne možemo means we cannot / we are not able to.

In Croatian, the negative particle ne is usually written separately from the verb.

So you get:

• ne mogu
• ne želim
• ne idemo
• ne možemo

That is why it is ne možemo, not one word.

A few very common negative forms are exceptions and are written together, such as:

• nisam
• nemam
• neću

But with moći, the normal spelling is separate: ne mogu, ne možeš, ne možemo, etc.

Because moći is a modal verb, and modal verbs in Croatian are normally followed by an infinitive.

So the structure is:

• možemo ostati = we can stay
• ne možemo ostati = we cannot stay

This works much like English:

• we can stay
• we cannot stay

In standard Croatian, this infinitive structure is the normal one. A learner may sometimes hear da + present in neighboring varieties, but standard Croatian prefers možemo ostati, not možemo da ostanemo.

Ostati means to stay / remain. It is the perfective partner of ostajati.

A simple way to think about the difference:

• ostati = the action seen as a whole, or the result to remain / to stay
• ostajati = the ongoing, repeated, or habitual idea to keep staying / to be remaining

In this sentence, ostati is natural because the speaker is talking about whether staying is possible at all, or for some further period.

Compare:

• Ne možemo ostati ovdje.
  We can't stay here.

• Ne možemo ostajati ovdje svako ljeto.
  We can't keep staying here every summer.

So ostati is the normal choice in your sentence.

Još is a very flexible word, and that is exactly why learners often find it tricky.

Depending on context, još can mean things like:

• still
• yet
• more
• another
• longer
• any longer

In a sentence like this, it often adds the idea of more time / longer / any longer.

So the important point is:

Do not try to match još to only one English word every time.
Its meaning depends a lot on context and word order.

Not always. English can't is ambiguous:

• it can mean not able
• or not allowed

Croatian usually separates those ideas more clearly.

• ne možemo = we can't / we are unable / it isn't possible
• ne smijemo = we may not / we aren't allowed

So if the problem is permission, Croatian often uses:

• Ne smijemo ostati ovdje.
  We are not allowed to stay here.

If the problem is possibility or ability, then:

• Ne možemo ostati ovdje.
  We can't stay here.

Ovdje means here, and it is an adverb of place.

Because it is an adverb, it does not change for case. So there is no nominative, accusative, etc. to worry about here.

That makes it simpler than nouns and adjectives.

You may also hear:

• tu = here / there, depending on context
• ovdje = here

In standard Croatian, ovdje is completely normal and neutral.

Yes. Croatian word order is fairly flexible, but changing it usually changes the focus or emphasis.

For example:

• Ne možemo još ostati ovdje.
• Još ne možemo ostati ovdje.
• Ovdje ne možemo još ostati.

These are not all identical in nuance.

A useful tendency to notice:

• Još ne možemo... often sounds more like still not / not yet
• Ne možemo još ostati... often sounds more like can't stay any longer / can't stay more

Context decides the final meaning, but word order helps guide the listener toward the intended nuance.

So yes, the order can change, but the original sentence is a natural, grammatical Croatian sentence.