Learn Hardcore Indonesian: Selain keluarga, beberapa pelanggan toko kecil itu juga tetangga kami. - Besides family, several customers of that small shop are also our neighbors.

Inclusive: Selain keluarga, ... juga ... = besides/as well as.
Exclusive: Selain keluarga, tidak/tiada/nyaris tak ... ≈ except for. You could also use kecuali for an unambiguously exclusive meaning.

Is the comma after Selain keluarga necessary?

Recommended but not mandatory. Selain keluarga is a fronted introductory phrase; a comma mirrors the spoken pause and improves readability: Selain keluarga, ...

Can I say selain dari keluarga?

You can, but selain keluarga is preferred in standard/formal style. Selain dari appears in colloquial speech and in set phrases like selain dari itu (“apart from that”). With a simple noun, drop dari.

Why is there no “to be” verb? Should I add adalah or merupakan?

Indonesian often omits a copula in nominal predicates. All of these are grammatical:

Neutral, common: ... juga tetangga kami.
More formal: ... juga merupakan tetangga kami.
Formal/definitional: ... juga adalah tetangga kami.

Notes:

adalah and merupakan are more common in writing.
Use them before a noun phrase, not before adjectives.

Where should juga go? Could it be at the end?

Common placements:

Before the predicate: ... juga tetangga kami. (natural, neutral focus)
At the end: ... tetangga kami juga. (adds a slight “as well” afterthought)

Placing juga before the subject (e.g., juga beberapa pelanggan...) shifts the meaning to “also, some customers...” comparing subjects across sentences.

What does itu do in toko kecil itu, and where does it go?

Itu is a distal demonstrative (“that/the aforementioned”). It follows the entire noun phrase:

toko kecil itu = that small shop / the small shop already known
The demonstrative comes after the noun phrase, not before it.

Why is it toko kecil and not kecil toko?

In Indonesian, adjectives typically follow the noun:

toko kecil = small shop For contrastive emphasis you can use yang: toko yang kecil itu (“the one that is small,” contrasted with another).

Is pelanggan toko kecil itu the same as pelanggan dari/di toko kecil itu?

Not exactly:

pelanggan toko kecil itu = customers of that small shop (inherent relationship; most natural)
pelanggan dari toko kecil itu = customers from that shop (slight “from” nuance)
pelanggan di toko kecil itu = customers at that shop (location-based, e.g., physically there)

What’s the difference between pelanggan, langganan, and nasabah?

pelanggan = customer/client (general)
langganan = “regular/favorite” when modifying a noun (e.g., warung langganan = our go-to stall); as a noun it can mean subscriber/regular.
nasabah = client of a bank/insurance/co-op (not used for shops).

Can I say beberapa orang pelanggan? What about para pelanggan?

beberapa pelanggan is already correct and natural.
beberapa orang pelanggan is also acceptable and can stress “people,” but it’s often unnecessary.
para pelanggan means “the customers (as a group)” and is formal; don’t combine para with numbers/quantifiers (so not para beberapa pelanggan).

Do I need to mark plural on tetangga? Should it be tetangga-tetangga?

No plural marking is required. tetangga can be singular or plural; beberapa already signals plurality. tetangga-tetangga (reduplication) is possible to emphasize plurality, but it’s usually not needed here.

Why is it kami and not kita? Can I say tetangga kita?

kami = we/us, excluding the listener.
kita = we/us, including the listener. Use kami if the listener isn’t part of the group; use kita if the listener is included (e.g., talking to a fellow neighbor).

Does keluarga here mean “our family”? Should I make it explicit?

On its own, keluarga is generic and relies on context; it often implies “(our) family” from the speaker’s perspective. To be explicit, use:

Selain keluarga kami, ... or
Selain anggota keluarga kami, ... (more precise: “family members”)

Could I use pun instead of juga?

Yes, but pun is more formal/literary and comes right after the element it adds to:

Selain keluarga, beberapa pelanggan toko kecil itu pun tetangga kami. You wouldn’t put pun at the very end like juga.

Can I drop itu in toko kecil itu? Does it change the meaning?

Yes. Without itu, toko kecil is non-specific (“a small shop” in general). With itu, it’s specific/known (“that small shop” or “the small shop we’ve been talking about”).

Can I move Selain keluarga to the end?

Yes: Beberapa pelanggan toko kecil itu juga tetangga kami, selain keluarga. Fronting it (with a comma) is slightly more natural and sets the context up front.