Những sản phẩm này ở các cửa hàng.

In Vietnamese, demonstratives such as này (this/these) usually come after the noun.

So:

• sản phẩm này = this product
• những sản phẩm này = these products

This is a very common word order pattern in Vietnamese:

• cuốn sách này = this book
• người đó = that person
• cái bàn kia = that table over there

So even though English says these products, Vietnamese says something more like products these.

Những is a plural marker. It tells you that sản phẩm is plural: products, not product.

So:

• sản phẩm = product / products, depending on context
• những sản phẩm = products
• những sản phẩm này = these products

Vietnamese nouns often do not have to change form for singular vs. plural. A noun can stay the same, and context tells you the number. But adding những makes the plural meaning clearer.

Yes, both can mark plurality, but they are not exactly identical.

A simple learner-friendly way to think about them is:

• những = plural, often some / a number of / these
• các = plural, often all the / various / multiple members of a group

In this sentence:

• những sản phẩm này = these products
• các cửa hàng = the stores / stores / various stores

Why this combination?

• những works very naturally with này for these products
• các cửa hàng suggests multiple stores as a group or category

In real Vietnamese, the distinction can be subtle, but that is the basic idea.

Because Vietnamese often does not use a separate verb like English to be in location sentences.

English:

• These products are in the stores.

Vietnamese:

• Những sản phẩm này ở các cửa hàng.

Here, ở handles the location idea, so you do not need a separate word meaning are.

Also, you would not normally use là here.
Là is not the normal choice for location.

So:

• correct: Những sản phẩm này ở các cửa hàng.
• unnatural/wrong for location: Những sản phẩm này là ở các cửa hàng.

Ở usually means at, in, or located at/in, depending on context.

In this sentence, it connects the products with their location:

• ở các cửa hàng = in the stores / at the stores

So ở is doing the work of expressing location.

Examples:

• Tôi ở nhà. = I am at home.
• Cô ấy ở trường. = She is at school.
• Sách ở trên bàn. = The book is on the table.

In your sentence, ở is best understood as are in / are at.

It can depend on context.

Các cửa hàng can mean:

• the stores if the stores are understood from context
• stores / various stores in a more general sense

Vietnamese often relies more on context than English for definiteness. So các cửa hàng does not always map perfectly to either the stores or stores.

If someone is talking generally about where these products can be found, ở các cửa hàng may sound like in stores.
If the stores are already known in the conversation, it may sound more like at the stores or in the shops.

Not literally. The sentence as written mainly says that the products are at / in stores, meaning their location.

However, in some contexts, a listener might infer the practical meaning these products are available in stores.

If you want to say These products are sold in stores more clearly, Vietnamese would usually say something like:

• Những sản phẩm này được bán ở các cửa hàng.

Here:

• được bán = are sold

So:

• Những sản phẩm này ở các cửa hàng. = These products are in/at stores.
• Những sản phẩm này được bán ở các cửa hàng. = These products are sold in stores.

Sometimes yes, but the meaning would become less specific.

Compare:

• Sản phẩm này ở cửa hàng. = This product is at the store.
• Những sản phẩm này ở các cửa hàng. = These products are in the stores / in stores.

Vietnamese often allows nouns without plural marking, because number can be understood from context. But if you want to be clear that there are multiple products and multiple stores, những and các help.

So they are not always grammatically required, but they are useful for precision.

Yes, it is natural and standard.

A very common pattern is:

• những + noun + này

So:

• những sản phẩm này = these products
• những cuốn sách này = these books
• những người này = these people

You may also see other ways to express plurality in Vietnamese, but for a learner, những + noun + này is a very solid pattern to remember for these + plural noun.

The structure is:

Những sản phẩm này + ở + các cửa hàng
subject/topic + location marker/predicate + place

So it works like:

• These products
  • are in/at
    • the stores

A useful pattern to remember is:

[noun phrase] + ở + [place]

Examples:

• Tôi ở nhà. = I am at home.
• Cô ấy ở văn phòng. = She is at the office.
• Những sản phẩm này ở các cửa hàng. = These products are in the stores.