Tenemos una grieta pequeña en la pared del baño.

Yes. Spanish often drops subject pronouns when the verb already makes the subject clear.

• Tenemos = we have
• The ending -emos tells you the subject is nosotros/nosotras

So Nosotros tenemos una grieta pequeña... is grammatically correct, but usually unnecessary unless you want emphasis or contrast.

Because tenemos means we have, while hay means there is/there are.

• Tenemos una grieta pequeña en la pared del baño = We have a small crack in the bathroom wall
• Hay una grieta pequeña en la pared del baño = There is a small crack in the bathroom wall

Both can be natural, but they are slightly different in focus:

• tenemos focuses on our situation/problem
• hay focuses on the existence of the crack

Grieta means crack, especially a visible split or opening in a surface such as a wall.

In this sentence, it is the normal word for a crack in a wall. Depending on context, Spanish can also use words like:

• fisura = fissure, hairline crack, often more technical
• raja = split/crack, sometimes more informal depending on context

But grieta is a very common and natural choice here.

Both are possible, but the position of the adjective changes the feel slightly.

• una grieta pequeña = a small crack
  This is the most neutral, literal description.
• una pequeña grieta = a small crack
  This can sound a bit more descriptive or subjective, sometimes slightly more literary or emphatic.

In everyday speech, Spanish often puts descriptive adjectives after the noun, so grieta pequeña is very normal.

Because Spanish usually uses the definite article more often than English.

• la pared = the wall

Even where English might say in the bathroom wall, Spanish naturally says en la pared del baño.

Spanish often prefers:

• the wall
• the bathroom rather than leaving those nouns bare.

Because del is the contraction of de + el.

• de el baño becomes del baño

So:

• la pared del baño = the wall of the bathroom / the bathroom wall

This contraction is mandatory in standard Spanish.

The only common exception is when el is part of a proper name:

• de El Escorial (not del Escorial)

Spanish usually expresses this kind of idea with noun + de + noun.

• la pared del baño = literally the wall of the bathroom

English often uses one noun to modify another:

• bathroom wall
• kitchen door
• bedroom window

Spanish usually prefers:

• la pared del baño
• la puerta de la cocina
• la ventana del dormitorio

So this structure is very common and natural.

En usually means in, on, or at, depending on context.

Here:

• en la pared = in/on the wall

With cracks, Spanish commonly uses en because the crack is understood as being in the surface of the wall.

So:

• una grieta en la pared = a crack in the wall

That is the standard way to say it.

Yes, absolutely.

That version is also correct:

• Tenemos una pequeña grieta en la pared del baño

Compared with una grieta pequeña, it can sound slightly more like you are highlighting the fact that the crack is small. The difference is subtle, and both are natural.

Because Spanish often does not use possessives when ownership is already obvious from context.

If you say:

• Tenemos una grieta pequeña en la pared del baño

it is already clear that you mean the bathroom wall in the place connected to we have.

Using nuestra is possible, but it is often unnecessary:

• Tenemos una grieta pequeña en nuestra pared del baño sounds less natural
• Tenemos una grieta pequeña en la pared de nuestro baño is possible, but usually only if you need to stress that it is our bathroom

Spanish prefers the simpler version unless the possession needs emphasis.

Yes. Baño is very common and completely natural in Spain.

You may also hear:

• cuarto de baño = bathroom
• aseo = toilet/restroom, sometimes smaller or more formal depending on context

In this sentence, baño is perfectly normal everyday Spanish.

You would make the noun and adjective plural:

• Tenemos unas grietas pequeñas en la pared del baño.

Changes:

• una → unas
• grieta → grietas
• pequeña → pequeñas

This is adjective agreement: the adjective must match the noun in gender and number.

It is pronounced roughly like GRYE-ta.

A simple breakdown:

• gri- sounds like gree blended quickly with a y glide
• -e-
• -ta

The stress is on the first syllable:

• GRIE-ta

In standard Spanish pronunciation, the r is a single tapped r, not a strong English r.