Learn Hardcore Indonesian: Ibu memutuskan duduk di ruang tamu, sementara sebagian tim tetap bekerja. - Mother decided to sit in the living room, while part of the team kept working.

Family context: ibu ≈ “mother” (often “Mom” in translations).
As a respectful title/address for an adult woman: Ibu ≈ “Ma’am/Mrs.” (e.g., Ibu Siti).
To make “my/your/her mother” explicit: use possessives like ibuku/ibu saya (my mother), ibumu/ibu kamu (your mother), ibunya (his/her/their mother).

Because Indonesian has no articles, bare Ibu can be ambiguous without context. In everyday speech, people also shorten it to Bu when addressing someone.

Should it be memutuskan duduk or memutuskan untuk duduk?

Both are understandable, but memutuskan untuk duduk is the standard, most natural form in neutral/formal Indonesian. Dropping untuk (so: memutuskan duduk) happens in casual speech or headlines, but many speakers find it a bit clipped. Safest choice: Ibu memutuskan untuk duduk di ruang tamu.

Why is there a comma before sementara?

Because sementara here is a conjunction linking two independent clauses. Indonesian typically uses a comma to separate such clauses for readability:

… duduk di ruang tamu, sementara sebagian …
The comma is recommended but you will see it omitted in very informal writing.

What’s the difference between sementara, sedangkan, ketika, and sambil?

sementara = “while/whereas/meanwhile” for two events happening at the same time; can also show mild contrast.
- Saya belajar, sementara adik menonton TV. (I study while my younger sibling watches TV.)
sedangkan = “whereas/while,” primarily for contrast/comparison between two facts.
- Ayah suka kopi, sedangkan Ibu suka teh.
ketika = “when (at the time that),” neutral time clause, often past narratives but not limited to past.
- Ketika saya datang, mereka sudah pergi.
sambil = “while (doing),” same subject performing two simultaneous actions.
- Ibu duduk sambil membaca. (She sits while reading.)
  In your sentence there are two different subjects, so sambil would not fit.

Why tetap and not masih in tetap bekerja?

tetap = “remain/keep (doing something) despite change or expectation.” It emphasizes persistence or continuity in the face of potential interruption.
masih = “still” (temporal continuation), a neutral ongoing state without the nuance of resistance. Here, tetap bekerja suggests “kept on working (even though circumstances might suggest stopping).” masih bekerja would simply mean “are still working,” less contrastive.

Is sebagian tim natural, or should it be sebagian dari tim or sebagian anggota tim?

If you mean “some members of the team,” the clearest is sebagian anggota tim.
sebagian tim can be ambiguous: it might be read as “some teams” (if multiple teams exist) or “a portion of the team.” It’s used, but context must disambiguate.
sebagian dari tim is grammatical but a bit wordy; many prefer sebagian anggota tim for clarity.

A very natural revision would be: … sementara sebagian anggota tim tetap bekerja.

How do we know the tense? Is this past, present, or future?

Indonesian doesn’t inflect verbs for tense. Time is inferred from context or added time words:

Past: add tadi, kemarin, barusan, tadi malam, etc.
Present/progressive: use sedang (optional), or rely on context.
Future: add akan, nanti, besok, etc.

So your sentence could be past or present depending on the surrounding context.

Why di ruang tamu and not ke ruang tamu?

di marks a location (at/in/on): di ruang tamu = “in/at the living room.”
ke marks movement toward a place: ke ruang tamu = “to the living room.”
Your sentence describes where she sits (location), so di is correct. If you wanted the movement, you’d say something like Ibu pergi ke ruang tamu.

Why is di written separately here? When is di attached to a word?

di as a preposition meaning “at/in/on” is written separately: di ruang tamu.
di- as a passive-voice prefix attaches to verbs: ditulis, dikerjakan.
So: di ruang tamu (preposition) vs dibaca (passive verb).

Is ruang tamu the same as ruangan tamu or kamar tamu?

ruang tamu = the living room (fixed expression).
kamar tamu = guest bedroom.
ruangan means “an enclosed room/space” in general, but ruangan tamu is not the usual term for the living room. Stick with ruang tamu.

Can I start with the second clause: Sementara sebagian …, Ibu …?

Yes. Both orders are fine:

Ibu memutuskan untuk duduk di ruang tamu, sementara sebagian anggota tim tetap bekerja.
Sementara sebagian anggota tim tetap bekerja, Ibu memutuskan untuk duduk di ruang tamu.

Keep the comma to separate the clauses.

How would I say “my mother” explicitly?

Use a possessive:

ibuku / ibu saya = my mother
ibumu / ibu kamu = your mother
ibunya = his/her/their mother
Example: Ibu saya memutuskan untuk duduk di ruang tamu …

Why is there no “the” before ruang tamu or tim?

Indonesian has no articles (“a/an/the”). Definiteness is understood from context or clarified with demonstratives/possessives if needed:

ruang tamu itu = that/the living room (specific)
tim tersebut = that/the team (aforementioned one)

Could I use memilih instead of memutuskan?

memutuskan = “to decide (after consideration),” slightly more formal/decisive.
memilih = “to choose/select,” focusing on picking one option.
Both can work, but memutuskan (untuk) duduk emphasizes the act of making a decision; memilih (untuk) duduk emphasizes the selection among options. Either is fine stylistically.

What’s the difference between sementara and sementara itu?

sementara (as a conjunction) links two clauses happening at the same time or in mild contrast: … duduk, sementara … bekerja.
sementara itu is an adverbial connector meaning “meanwhile” at the start of a sentence/paragraph: Sementara itu, sebagian tim tetap bekerja.
Think of sementara itu as a discourse connector, not a clause linker.