Ambos baralharam o baralho.

Ambos means both.

It refers to two people or two things together. In this sentence, it means that the two people both shuffled the deck.

A few useful points:

• ambos = masculine or mixed-gender plural
• ambas = feminine plural

Examples:

• Ambos chegaram cedo. = Both arrived early.
• Ambas estavam cansadas. = Both were tired.

Baralharam is the 3rd person plural preterite form of baralhar.

That means:

• baralhar = to shuffle
• baralharam = they shuffled

It matches ambos, because ambos is plural.

Very roughly:

• eu baralhei = I shuffled
• tu baralhaste = you shuffled
• ele/ela baralhou = he/she shuffled
• eles/elas baralharam = they shuffled

So Ambos baralharam o baralho literally works as:

• Both shuffled the deck

Portuguese can use ambos on its own when it is already clear who the two people or things are.

So:

• Ambos baralharam o baralho. = Both shuffled the deck.

But you can also say:

• Ambos os jogadores baralharam o baralho. = Both players shuffled the deck.

Using ambos alone is perfectly natural when the context already tells us who the two are.

Both can mean both, but they are not always used in exactly the same way.

• ambos is a bit more formal or literary
• os dois is often more everyday and conversational

So these are both possible:

• Ambos baralharam o baralho.
• Os dois baralharam o baralho.

In normal speech, many speakers would very naturally use os dois.

They are related words:

• baralho = deck of cards
• baralhar = to shuffle

So the sentence has a kind of word repetition:

• Ambos baralharam o baralho.

Literally, it is like:

• Both shuffled the deck

This is completely normal in Portuguese. It may sound repetitive to an English speaker, but it is not strange.

Also, baralho can sometimes mean cards more generally, depending on context.

Yes, Ambos baralharam is grammatically possible if the object is understood from context.

But baralhar usually makes the listener expect something that is being shuffled, such as:

• o baralho = the deck
• as cartas = the cards

So:

• Ambos baralharam. = Both shuffled.
  This works only if it is already obvious what they shuffled.
• Ambos baralharam o baralho. = Both shuffled the deck.
  This is clearer and more complete.

Yes. Besides the literal meaning to shuffle, baralhar can also mean to mix up or to confuse.

Examples:

• Baralhaste as folhas todas. = You mixed up all the sheets.
• Isso baralha-me. = That confuses me.

So it is a useful verb outside card-playing too.

Portuguese often leaves out subject pronouns because the verb form already shows who the subject is.

Here:

• baralharam already tells us the subject is they
• ambos makes it even clearer: both

So eles is unnecessary.

You could say:

• Eles ambos baralharam o baralho.

But that is less natural in many contexts than simply:

• Ambos baralharam o baralho.

Yes. Ambos can refer to two people or two things.

Examples:

• Ambos os livros são bons. = Both books are good.
• Ambos chegaram tarde. = Both arrived late.

In your sentence, it most naturally refers to two people, because the action is shuffling the deck.

The most important feature is lh, which is a special Portuguese sound.

• baralho is approximately buh-RA-lyoo in a rough English-style guide
• the lh sound is like the lli in some pronunciations of million, but this comparison is only approximate

A few pronunciation notes for European Portuguese:

• unstressed a is often reduced
• lh is a palatal sound, written lh
• the final o is often pronounced more like u

So baralho does not sound like English bar-AL-ho.

The sentence is grammatical in both European and Brazilian Portuguese.

However, there is a vocabulary difference worth knowing:

• In Portugal, baralhar is the standard everyday verb for to shuffle
• In Brazil, embaralhar is also very common for to shuffle, though baralhar exists too

So in European Portuguese, Ambos baralharam o baralho sounds perfectly normal.

Normally, no. Ambos and os dois already mean nearly the same thing, so using both together is usually redundant.

Natural options are:

• Ambos baralharam o baralho.
• Os dois baralharam o baralho.

But not usually:

• Ambos os dois baralharam o baralho.

A learner should generally avoid combining them.

Yes, but the original order is the most straightforward.

Most neutral:

• Ambos baralharam o baralho.

Also possible in some contexts:

• Os dois baralharam o baralho.
• Baralharam ambos o baralho.
  This is possible, but it sounds more marked or literary.

So for everyday use, Ambos baralharam o baralho is a very good model.