Después de la mudanza, tuvimos que apilar las cajas en el pasillo y deshacer solo la maleta más pequeña.

Because después needs de before a noun.

• después = after / afterward
• después de + noun = after + noun

So:

• después de la mudanza = after the move
• después de comer = after eating

You cannot normally say después la mudanza.

Mudanza usually means moving house or a move in the sense of changing homes.

So la mudanza here is not just any kind of movement. It specifically refers to the whole house move: packing, transporting things, arriving at the new place, and so on.

Very common related expressions are:

• hacer la mudanza = to do the move
• mudarse = to move house

Tuvimos que is the preterite of tener, and it fits because the sentence is talking about a specific, completed situation in the past.

• tuvimos que = we had to
• teníamos que = we used to have to / we were having to / we had to in an ongoing background sense

Here, the speaker is narrating what happened after the move as a completed event, so tuvimos que sounds natural.

Compare:

• Después de la mudanza, tuvimos que apilar las cajas...
  A specific thing we had to do then.

• Cuando vivíamos allí, teníamos que subir las cajas a mano.
  A repeated or background obligation.

Because after tener que, Spanish uses an infinitive.

The structure is:

tener que + infinitive

So:

• tuvimos que apilar = we had to stack
• tuvimos que deshacer = we had to unpack

In this sentence, one tuvimos que governs both verbs:

• tuvimos que apilar las cajas... y deshacer...

That is why both apilar and deshacer stay in the infinitive.

Literally, deshacer means to undo.

But with things like luggage, beds, or arrangements, Spanish often uses deshacer in an idiomatic way:

• hacer la maleta = to pack the suitcase
• deshacer la maleta = to unpack the suitcase

So the idea is: you undo what was packed.

This is a very natural expression in Spanish.

Spanish uses the definite article more often than English.

Here, each noun is understood as specific in context:

• la mudanza = the move we are talking about
• las cajas = the boxes from that move
• el pasillo = the hallway in that home/building
• la maleta más pequeña = the smallest suitcase among the relevant suitcases

English often drops the where Spanish keeps it, so this is very normal Spanish usage.

Because en gives the location where the boxes were stacked: in the hallway or in the corridor.

• en = in / on / at, depending on context
• el pasillo = the hallway / corridor

So apilar las cajas en el pasillo means the hallway is the place where the boxes ended up.

A learner may expect a, but a is more associated with movement toward a destination. Here the focus is the final location, so en is natural.

Solo and solamente can both mean only.

In this sentence, solo is just shorter and more natural in everyday use:

• deshacer solo la maleta más pequeña

As for the accent: modern standard spelling normally writes solo without an accent mark, even when it means only.

Older spelling often used sólo to distinguish it from solo meaning alone, but today the usual recommendation is solo unless a writer feels an accent is needed to avoid real ambiguity.

Here, no accent is needed.

Because in Spanish, adjectives usually come after the noun, and the normal superlative pattern is:

noun + más + adjective

So:

• la maleta más pequeña = the smallest suitcase

This is the standard, natural order.

la más pequeña maleta sounds unusual and literary or highly emphatic. A learner should normally use la maleta más pequeña.

It is the relative superlative: the smallest.

Literally:

• pequeña = small
• más pequeña = smaller / more small
• la maleta más pequeña = the smallest suitcase

Even though Spanish uses más + adjective, English often translates this as a superlative in context.

So you should understand la maleta más pequeña as the smallest suitcase, not just the smaller suitcase, unless the context is very specific and only two suitcases are being compared.

In this sentence, solo most naturally limits la maleta más pequeña.

So the meaning is:

• they stacked the boxes in the hallway
• and they unpacked only the smallest suitcase

It does not naturally mean that unpacking was the only action, because the sentence already says they also had to apilar las cajas.

So solo is best understood as modifying the noun phrase la maleta más pequeña.

Usually, yes. Pasillo commonly means hallway, corridor, or passage.

In this sentence, en el pasillo would normally be understood as in the hallway.

A useful distinction is:

• pasillo = corridor / hallway, a passage you walk through
• recibidor = entrance hall / foyer

So pasillo is the normal word if the boxes were stacked along an internal corridor.