En mi familia valoramos mucho los buenos modales en la mesa.

Because en mi familia is not the subject of the sentence. It means in my family or in my household, setting the context.

The real subject is an omitted we:

• (Nosotros) valoramos... = We value...

So the sentence is literally:

• In my family, we value good table manners a lot.

If you wanted my family to be the grammatical subject, you would say:

• Mi familia valora mucho los buenos modales en la mesa.

Both are correct, but they are structured differently.

It means in my family or in my household.

Spanish often uses en to place something within a group, setting, or social context:

• En mi familia... = In my family...
• En mi trabajo... = At/In my workplace...
• En casa... = At home...

So here it does not describe physical location. It introduces a general family custom or value.

Spanish normally drops subject pronouns when they are clear from the verb ending.

• valoramos already tells you the subject is we
• so nosotros valoramos is usually unnecessary

Spanish prefers:

• Valoramos mucho...

instead of:

• Nosotros valoramos mucho...

You would add nosotros only for emphasis, contrast, or clarity.

Because mucho here is an adverb meaning a lot or very much, and in Spanish it commonly goes after the verb.

So:

• valoramos mucho = we value a lot / we really value

This is the most natural word order.

Compare:

• Valoramos mucho los buenos modales = natural
• Mucho valoramos... = possible, but poetic, formal, or unusual in everyday speech

Spanish often uses the definite article with nouns when speaking about things in a general sense.

So:

• los buenos modales = good manners

The article does not necessarily mean the in a very specific sense here. It is just the normal Spanish way to talk about the concept.

Without los, the phrase would sound incomplete or unnatural in this sentence.

When modales means manners, it is normally used in the plural:

• los modales = manners
• buenos modales = good manners
• malos modales = bad manners

The singular modal usually means something else, so for this idea you should learn it as a plural noun.

This is similar to some English words that are commonly used in only one number.

They overlap, but they are not exactly the same.

• buenos modales = good manners, polite behavior
• educación = education, but also politeness / good upbringing depending on context
• buenas maneras = good manners, good ways, also possible but a bit less common in this exact context

In this sentence, buenos modales is very natural because it refers to polite behavior, especially in a social setting like eating.

Because en la mesa means at the table or while at the table, which fits the idea of table manners.

• en la mesa = at the table
• a la mesa = to the table

So:

• buenos modales en la mesa = good manners at the table
• ¡A la mesa! = To the table! / Come to the table!

If you used a la mesa here, it would sound like movement toward the table, not behavior during the meal.

Yes, absolutely.

That version makes mi familia the grammatical subject:

• Mi familia valora... = My family values...

The original:

• En mi familia valoramos... = In my family, we value...

The difference is mainly one of perspective:

• Mi familia valora... talks about the family as a unit
• En mi familia valoramos... sounds more like the speaker is speaking from inside the family and includes themself more directly

Yes, you could use apreciar, but valorar is especially natural here.

• valorar = to value, consider important
• apreciar = to appreciate, esteem

In this sentence, valorar works very well because the idea is that good table manners are an important family value.

So:

• valoramos mucho los buenos modales = we place a lot of importance on good manners

That sounds very idiomatic in Spanish.

No. In this sentence, en la mesa means at the table, not on top of the table.

This is one of those expressions where Spanish uses en more broadly than English learners may expect.

Compare:

• comer en la mesa = eat at the table
• estar sentado a la mesa = be seated at the table
• poner el libro sobre la mesa = put the book on the table

If you want to mean physically on top of the table, sobre la mesa is clearer.

Yes, it sounds completely natural in Spain, and it is also understandable everywhere else.

Nothing in it is strongly regional, but los buenos modales en la mesa sounds very standard and idiomatic in Peninsular Spanish.

A speaker from another Spanish-speaking country would also understand it easily, though they might choose slightly different wording depending on style or region.