Tanto la blusa como la rebeca estaban ya preparadas sobre la cama, al lado de la colcha.

It means both ... and ....

So:

• Tanto la blusa como la rebeca = both the blouse and the cardigan

This structure links two elements in a balanced way. It is very common in Spanish.

You can also use it with other kinds of words, not just nouns:

• Tanto Ana como Luis llegaron tarde = both Ana and Luis arrived late
• Es tanto útil como bonito = it is both useful and nice

In this sentence, it joins two things: la blusa and la rebeca.

Because the subject is made up of two things:

• la blusa
• la rebeca

When two nouns are joined by tanto ... como ..., Spanish normally treats them as a plural subject, so the verb goes in the plural:

• Tanto la blusa como la rebeca estaban...

If there were only one item, it would be singular:

• La blusa estaba preparada

Because preparadas agrees with the two nouns it describes.

Both nouns are:

• la blusa = feminine
• la rebeca = feminine

Together, they form a feminine plural group, so the adjective must also be feminine plural:

• preparadas

Compare:

• La blusa estaba preparada = singular feminine
• El jersey y el abrigo estaban preparados = plural masculine
• La blusa y el jersey estaban preparados = mixed group, so masculine plural

Because estaban is the imperfect, and here it describes a state or background situation.

The sentence is not focusing on the action of becoming ready. It is describing how things were at that moment:

• the blouse and cardigan were already laid out / were ready

Using estuvieron would sound more like a completed, bounded situation over a period of time, which is less natural here.

So:

• estaban preparadas = they were in a ready state
• estuvieron preparadas = they were ready for some limited time

In description, estaban is the normal choice.

Yes, both are possible:

• Ya estaban preparadas
• Estaban ya preparadas

Both mean basically the same thing: they were already ready / already laid out.

The difference is mostly one of style and emphasis:

• Ya estaban preparadas is perhaps the more neutral, everyday order
• Estaban ya preparadas can sound a bit more literary or slightly more focused on the state being already achieved

So the placement of ya is flexible.

Because sobre means on top of or upon the bed.

That fits clothes being laid out on the surface of the bed.

• sobre la cama = on the bed
• en la cama = in bed

In casual speech, en la cama can sometimes mean on the bed, depending on context, but it can also suggest being inside the bed or in bed as a person would be. So sobre la cama is more precise here.

In Spain, rebeca commonly means cardigan.

It is a normal everyday word in Peninsular Spanish. In other Spanish-speaking places, you may hear other words more often, such as:

• cárdigan
• suéter
• chaqueta de punto, depending on region and style

So if you are learning Spanish from Spain, rebeca is a useful word to know.

Al is the contraction of a + el.

But here, the el does not refer to colcha. It belongs to the expression lado:

• al lado de = at the side of / next to

So the structure is:

• a + el lado de la colcha
• shortened to al lado de la colcha

That is why you get al, even though colcha is feminine.

You should think of al lado de as a fixed expression meaning next to.

In this context, colcha usually means something like:

• bedspread
• coverlet
• sometimes quilt, depending on context

It is the covering on the bed, usually the visible outer layer. So:

• al lado de la colcha = next to the bedspread / next to the quilt

The exact English word can vary a bit depending on the type of bedding.

Because in Spanish, when you mention two specific nouns together, each one usually keeps its own article:

• la blusa y la rebeca

That is the most natural pattern here. Since these are two distinct, specific items of clothing, repeating la sounds normal.

With tanto ... como ..., this repetition is especially standard:

• Tanto la madre como el padre
• Tanto el vino como la cerveza

Dropping the second article is not the usual choice here.

Not necessarily in the broad English sense.

With clothes or objects, estar preparado/a often means:

• laid out
• made ready
• set out for use

So the sentence probably means that the blouse and cardigan had already been placed on the bed, ready to be worn or used.

That is a very natural use of preparado/a in Spanish.

Yes. Junto a and al lado de can both mean next to.

• al lado de la colcha
• junto a la colcha

In many contexts, they are interchangeable.

A slight difference is that:

• al lado de is very literal and transparent: at the side of
• junto a can sound a bit more compact or slightly more formal, depending on context

But in this sentence, either would work grammatically.