Learn Hardcore Malay: Adik-beradik saya berebut tempat duduk di sofa. - My siblings fight over a seat on the sofa.

adik by itself = younger sibling (or sometimes used affectionately for someone younger)
beradik here comes from reduplication of adik and indicates plurality; with the hyphen, adik-beradik is treated as a fixed expression meaning siblings.

So adik-beradik saya = my siblings, not my younger sibling.

Why is there a hyphen in adik-beradik? Could we just write adik beradik?

In Malay, a hyphen is commonly used in reduplication, where a word is repeated to change or refine its meaning.

adik → single younger sibling
adik-adik → younger siblings (plural of adik)
adik-beradik → all brothers and sisters (siblings as a set), not just the younger ones

Adik-beradik is a set phrase and is normally written with a hyphen. Writing adik beradik (with a space) would look incorrect or at least non-standard in formal writing.

What role does saya play here, and why does it come after adik-beradik?

Saya means I / me and, when placed after a noun, it works like a possessive pronoun: my.

Word order in Malay noun phrases is usually:

[noun] + [possessor]

So:

adik-beradik saya = my siblings
rumah saya = my house
kawan saya = my friend(s)

You do not say saya adik-beradik to mean my siblings. That would sound like I am siblings, which is ungrammatical.

What does berebut mean, and how is it different from similar verbs?

Berebut means roughly to scramble for / to fight over / to compete for something, usually in a slightly chaotic way and involving more than one person.

In this sentence, berebut tempat duduk means are fighting over the seat.

Some related verbs:

rebut (without be-): to snatch / grab / wrest something from someone.
- Dia merebut buku itu dari tangan saya. = He snatched the book from my hand.
berebut: focus on several people competing for something.
- Mereka berebut mainan itu. = They are fighting over that toy.
merebutkan: can mean to make something an object of competition or to contest something.
- Mereka merebutkan jawatan itu. = They are competing for that position.

In your sentence, berebut is appropriate because several siblings are trying to get the same seat.

What does tempat duduk literally mean? Why not just say kerusi?

Literally:

tempat = place
duduk = to sit
tempat duduk = a place to sit → a seat

So tempat duduk focuses on the spot where you sit, not necessarily a single piece of furniture.

Kerusi = chair (a specific item of furniture).

In context:

berebut tempat duduk di sofa = fighting over who gets to sit where on the sofa / a seat on the sofa.
If you said berebut kerusi, it sounds more like fighting over a (particular) chair, not about positions on a sofa.

Both are correct Malay; they just focus on slightly different things.

Why is it di sofa, not di atas sofa?

di = at / on / in (general preposition for location)
atas = on top of

Di sofa is already understood as on/at the sofa in everyday speech, because sofa is something you sit on.

You can say:

di sofa = at/on the sofa (normal, natural)
di atas sofa = literally on top of the sofa; also correct, but slightly more specific and a bit more formal-sounding in this context.

In conversation, di sofa is perfectly natural.

How do we know if this sentence is present, past, or future tense?

Malay verbs do not change form for tense. Berebut stays the same for past, present, or future. The time is understood from context or from time words added to the sentence.

Your sentence on its own can mean:

My siblings are fighting over the seat on the sofa. (right now)
My siblings were fighting over the seat on the sofa. (earlier)

You can add time markers for clarity:

Tadi, adik-beradik saya berebut tempat duduk di sofa.
Earlier, my siblings were fighting over the seat on the sofa.
Sekarang, adik-beradik saya sedang berebut tempat duduk di sofa.
Right now, my siblings are fighting over the seat on the sofa.
Nanti, adik-beradik saya akan berebut tempat duduk di sofa.
Later, my siblings will fight over the seat on the sofa.

What is the basic word order of this sentence?

The structure is standard Malay S–V–O–(Place):

Subject: adik-beradik saya (my siblings)
Verb: berebut (are fighting over / scrambling for)
Object: tempat duduk (a seat / the seat)
Place phrase: di sofa (on the sofa)

So the pattern is:

[Who] + [does what] + [to/for what] + [where]
Adik-beradik saya + berebut + tempat duduk + di sofa.

Is sofa a Malay word or a loanword? Could I say something else instead?

Sofa is a widely accepted loanword (from European languages) in Malay and is completely normal in modern usage.

Alternatives:

sofa = sofa / couch (most common)
kerusi panjang = long chair / bench (can be used but sounds a bit old‑fashioned or descriptive)
bangku = bench/stool (not the same as a sofa)

In everyday Malay, sofa is the natural word to use for a couch.

Could we leave out saya and just say Adik-beradik berebut tempat duduk di sofa?

You can say Adik-beradik berebut tempat duduk di sofa, but the meaning changes slightly:

Adik-beradik saya = my siblings (specific group, belonging to me)
Adik-beradik (without saya) = siblings in general, or context-dependent (e.g. siblings in a particular family already being discussed)

In practice, if you are clearly talking about your own family, people might still understand that you mean your siblings, but adding saya is clearer and more natural when you first mention them.

Is there any plural marker needed, like saying adik-beradik-adik or adik-beradik semua?

No extra plural marker is needed for adik-beradik itself:

adik-beradik already implies plural (siblings as a group).
You do not say adik-beradik-adik or adik-beradik-saya with extra reduplication or suffixes.

You can add semua to emphasize all of them:

Semua adik-beradik saya berebut tempat duduk di sofa.
All of my siblings are fighting over the seat on the sofa.

Is this sentence formal or informal? Would it be okay in writing?

The sentence Adik-beradik saya berebut tempat duduk di sofa. is neutral and fine in both speech and writing. It is suitable for:

everyday conversation
informal writing (messages, diaries)
even neutral/formal narrative (e.g. a story, an essay about family)

A slightly more formal or explicit version might be:

Adik-beradik saya berebut untuk mendapatkan tempat duduk di sofa.
My siblings are competing to get a seat on the sofa.

But your original sentence is already perfectly acceptable Malay.