Nos quedamos dentro del establo hasta que pasó la tormenta.

Nos is the reflexive/object pronoun used with quedarse.

• quedar on its own can mean things like to remain, to be left, or to arrange
• quedarse often means to stay or to remain somewhere

So:

• quedamos = we arranged / we remained / we were left, depending on context
• nos quedamos = we stayed

In this sentence, nos is necessary because the verb being used is quedarse, not just quedar.

Both can sometimes translate as we stayed, but they are not exactly the same.

• nos quedamos focuses on remaining in a place
• estuvimos simply says we were somewhere for a period of time

So:

• Nos quedamos dentro del establo = we stayed/remained inside the stable
• Estuvimos dentro del establo = we were inside the stable

In this sentence, quedarse sounds natural because the idea is that we remained there until the storm passed.

The preterite is used because this is seen as a completed action in the past.

The sentence describes a finished event:

• we stayed in the stable
• the storm passed
• the whole situation is over

So nos quedamos means we stayed as a completed past action.

If you used the imperfect, nos quedábamos, it would suggest something more ongoing, habitual, or backgrounded, and it would sound less natural here unless more context was added.

Pasó is also in the preterite because the storm finished passing. It marks the endpoint.

• hasta que pasó la tormenta = until the storm passed

The imperfect pasaba would usually describe an ongoing action in the background, not the completed moment when the storm was over.

Here, the important idea is the end of the storm, so pasó fits better.

After hasta que, Spanish can use either the indicative or the subjunctive, depending on whether the action is viewed as real/completed or still pending.

Here, the whole sentence is about a past event that actually happened:

• the storm really did pass

So Spanish uses the indicative:

• hasta que pasó la tormenta

Compare:

• Nos quedaremos aquí hasta que pase la tormenta.
  = We’ll stay here until the storm passes.
  Here it has not passed yet, so subjunctive (pase) is used.

Both are possible, but they are slightly different in emphasis.

• en el establo = in the stable
• dentro del establo = inside the stable

Dentro de stresses being inside, perhaps for protection or contrast with being outside. In a sentence about a storm, that extra sense makes good sense.

So dentro del establo feels a bit more vivid: they stayed inside the stable until the storm passed.

Because de + el contracts to del in Spanish.

So:

• dentro de el establo → dentro del establo

This contraction is required in normal Spanish.

A similar contraction happens with:

• a + el → al

For example:

• al establo = to the stable

Spanish often uses the definite article more often than English does.

So la tormenta simply means the storm. In context, it refers to the specific storm they were waiting out.

Using the article here is completely natural in Spanish.

Yes. That is perfectly natural.

The difference is mainly one of emphasis:

• en el establo = in the stable
• dentro del establo = inside the stable

The version with dentro stresses the idea of being physically inside, which fits well with sheltering from a storm.

The basic verb is pasar = to pass.

Pasó is:

• third person singular
• preterite
• so it means he/she/it passed

In this sentence, the subject is la tormenta, which is singular:

• la tormenta pasó = the storm passed

Even though tormenta is feminine, the verb form does not change for gender, only for person and number.

Yes, Spanish word order is fairly flexible, though the original version is very natural.

Standard order:

• Nos quedamos dentro del establo hasta que pasó la tormenta.

You could also say:

• Hasta que pasó la tormenta, nos quedamos dentro del establo.

That version puts more focus on the time clause first. Both are grammatical, but the original is the more neutral everyday order.