Learn Hardcore Filipino: Masaya ang lola nilang nasa bahay ngayong gabi. - Their grandmother who is at home tonight is happy.

Masaya = the predicate (what is being said about someone: happy)
ang lola nilang nasa bahay ngayong gabi = the topic (the one being talked about)

So the literal structure is like:

Happy is their grandmother who is at home tonight.

Filipino normally does not use a separate word for is/are/am in this kind of sentence. The adjective masaya itself functions like is happy.

You can also say:

Ang lola nilang nasa bahay ngayong gabi ay masaya.

Here ay is an inversion marker that lets you put the topic first. It often feels more formal or written. But the meaning is the same: there’s still no separate is; masaya is still the part that means is happy.

What does ang do in ang lola nilang nasa bahay ngayong gabi?

Ang is a topic marker (often called the ang-marker). It marks the main noun phrase the sentence is talking about.

Very roughly, ang often corresponds to English the, but it really signals grammatical role (topic/focus) more than definiteness.

Some common markers:

ang – for common nouns in the singular
- ang lola = the grandmother
ang mga – for common nouns in the plural
- ang mga lola = the grandmothers
si – for a singular personal name
- si Maria
sina – for plural personal names
- sina Maria at Juan

So in Masaya ang lola nilang nasa bahay ngayong gabi, ang tells you that lola nilang nasa bahay ngayong gabi is the topic (the one that is happy).

What exactly does lola nilang mean, and how is it formed?

Break it down like this:

lola = grandmother
nila = their (third person plural possessive)
-ng = a linker (connecting word, from na)

Underlying form:

lola nila na nasa bahay ngayong gabi
their grandmother who is at home tonight

The linker na normally joins a noun to a modifier (another adjective, phrase, or clause). Here, nasa bahay ngayong gabi is a clause that modifies lola nila.

Because nila ends in a vowel, na attaches as -ng, giving:

nila + na → nilang

So we get:

lola nilang nasa bahay ngayong gabi
literally: their grandmother who is at home tonight

Why is it lola nilang nasa bahay… instead of lola nila nasa bahay…? Is something omitted?

What seems to be “missing” is just the linker na.

The fully separated version would be:

lola nila na nasa bahay ngayong gabi

This is perfectly grammatical, but in normal spelling and speech the na fuses with the preceding word:

nila na → nilang

So lola nila na nasa bahay… and lola nilang nasa bahay… are essentially the same structure; the second is just the standard contracted form.

Functionally, na / -ng here is connecting:

the possessed noun phrase lola nila
and
the modifier clause nasa bahay ngayong gabi (“who is at home tonight”)

What does nila mean here, and how is it different from sila and kanila?

These three are related pronouns, but they have different grammatical roles:

sila – they (subject / topic form)
- Sila ang mga apo. = They are the grandchildren.
nila – their / by them (genitive form)
- lola nila = their grandmother
- Binisita nila ang lola. = They visited the grandmother.
kanila – to/for them; theirs (oblique form)
- Para sa kanila. = For them.
- Sa kanila ang bahay. = The house is theirs.

In lola nilang nasa bahay…, nila is the possessive:

lola nila = their grandmother
lola nilang… = their grandmother who… (with the linker added)

What does nasa mean, and how is it different from sa?

Both are related to location, but they behave differently.

sa is a general location/direction marker:
- sa bahay = at/to the house
- Pumunta sila sa bahay. = They went to the house.
nasa works more like “to be located at”:
- Nasa bahay ang lola. = The grandmother is at home.

In the sentence lola nilang nasa bahay ngayong gabi:

nasa bahay = is at home / is in the house

So nasa already carries the idea of is at. That’s why you don’t need a separate is and why you don’t just say sa bahay there. Sa bahay by itself would just be a location phrase; nasa bahay is a whole predicate (be at home).

Could I just use sa bahay instead of nasa bahay here?

Not in the same way.

nasa bahay = is at home / is in the house (full predicate)
sa bahay = at the house / to the house (a prepositional phrase, not a predicate by itself)

In lola nilang nasa bahay ngayong gabi, nasa bahay ngayong gabi is acting like a little clause:

(who) is at home tonight

If you changed it to sa bahay ngayong gabi without nasa, it would sound like a fragment attached to lola and you’d lose the clear “is at” meaning.

You can, however, use sa bahay with another verb:

nakatira sa bahay = lives in the house
pumupunta sa bahay = goes to the house

Why is it ngayong gabi and not ngayon gabi or just ngayon?

Ngayon means now / today, but when it directly modifies another noun (like gabi), Filipino usually adds a linker.

The pattern is:

base word: ngayon = now / today
linker allomorph: -g (used after a word ending in n)
combined: ngayong + gabi

So:

ngayon = now, today
ngayong gabi = this evening / tonight (literally: now-linker night)

Other similar examples:

ngayong umaga = this morning
ngayong linggo = this week
ngayong buwan = this month

You can say just ngayon if you don’t specify the time of day:

Masaya ang lola nila ngayon. = Their grandmother is happy now / today.

But if you want tonight, ngayong gabi is the natural expression.

Can I move ngayong gabi to the beginning of the sentence?

Yes. Time expressions are quite flexible in Filipino. All of these are acceptable:

Masaya ang lola nilang nasa bahay ngayong gabi.
(neutral order; time at the end)
Ngayong gabi, masaya ang lola nilang nasa bahay.
(time is fronted for emphasis)
Masaya ngayong gabi ang lola nilang nasa bahay.
(time is attached more tightly to the predicate masaya)

There is a subtle difference in emphasis:

Ngayong gabi, masaya…
highlights tonight as the frame: As for tonight, their grandmother who is at home is happy.
Masaya ngayong gabi…
tends to emphasize that the happiness is specifically tonight, contrasting with other times.

The original Masaya … ngayong gabi is the most neutral-sounding for everyday speech.

Can I also say Ang lola nilang nasa bahay ngayong gabi ay masaya? Is that the same?

Yes, this is also correct.

Ang lola nilang nasa bahay ngayong gabi ay masaya.

Here:

Ang lola nilang nasa bahay ngayong gabi = topic
ay = inversion marker
masaya = predicate (is happy)

This version:

sounds a bit more formal or bookish,
is common in written Filipino, news, speeches, etc.

The meaning is still the same as:

Masaya ang lola nilang nasa bahay ngayong gabi.

The ay does not translate to English is; it just marks the inversion (Topic ay Predicate).

What exactly does nasa bahay ngayong gabi modify here: lola or masaya?

Grammatically, nasa bahay ngayong gabi modifies lola, not masaya.

The structure is:

Masaya
ang [lola nilang [nasa bahay ngayong gabi]].

So we have:

head noun: lola
possessor: nila (their)
modifier clause: nasa bahay ngayong gabi (who is at home tonight)

Overall meaning:

The grandmother who is at home tonight is happy.

If you wanted to emphasize more that the happiness is what’s specific to tonight (rather than the being-at-home part), you’d usually move ngayong gabi closer to masaya:

Masaya ngayong gabi ang lola nilang nasa bahay.
Ngayong gabi, masaya ang lola nilang nasa bahay.

In the original sentence, both the being at home and the happiness are understood to be true tonight, but syntactically nasa bahay ngayong gabi is inside the lola phrase.

Does lola always mean grandmother, or can it also mean an older woman in general?

Primarily:

lola = grandmother (like grandma / granny)

But in actual use, Filipinos also say lola to:

politely address or refer to an elderly woman, even if she’s not literally your grandmother.
- Siya ang lola sa kanto. = She’s the elderly lady on the corner.

Similarly:

lolo = grandfather / elderly man

In this particular sentence, because it’s their grandmother (lola nilang), the natural interpretation is the literal grandmother, not just any older woman.

How would the sentence change if we were talking about more than one grandmother, or about a different possessor (like our grandmother)?

Plural grandmothers:

Add mga to mark the plural:

Masaya ang mga lola nilang nasa bahay ngayong gabi.
= Their grandmothers who are at home tonight are happy.

Here:

ang mga lola = the grandmothers

Our grandmother:

There are two kinds of we/our in Filipino:

inclusive “our” (including the listener): natin
exclusive “our” (excluding the listener): namin

So you can say:

Masaya ang lola nating nasa bahay ngayong gabi.
= Our (yours and mine) grandmother who is at home tonight is happy.
Masaya ang lola naming nasa bahay ngayong gabi.
= Our (but not yours) grandmother who is at home tonight is happy.

The pattern is the same:

Masaya ang lola X‑ng nasa bahay ngayong gabi.
where X can be nila, natin, namin, mo, ko, etc.

What’s the difference between kanilang lola and lola nila? Which sounds more natural here?

Both express their grandmother, but they differ in form and flavor:

kanilang lola – kanilang comes before the noun
- feels a bit more formal or emphatic
- like English their grandmother (pre-nominal)
lola nila – nila comes after the noun
- very common and natural in everyday speech
- like English grandmother of theirs in structure, but normally just translated their grandmother

In your sentence, you could say:

Masaya ang kanilang lola na nasa bahay ngayong gabi.
Masaya ang lola nilang nasa bahay ngayong gabi.

Both are correct. For ordinary conversation, lola nila / lola nilang… is more typical and sounds a bit more casual/natural. Kanilang lola may sound slightly more formal or written.