Question: Adjectives

Yes, we commonly express the modifier/adjective of a plural noun that way because it is the grammatically correct way. It is also used with nouns with a “ma-”, “man-” or “mang-” prefix.Mabaít SIYA = HE/SHE is good/kind
Mababaít SILA = THEY are good/kind. (Note that “siya” becomes “sila”.)In casual conversations or informal writing, some of us may incorrectly use the adjective in its singular form. So, saying “mabait SILA” is also common. If the group is small, the plurality would normally be understood as true for everyone in the group. However, if the group is big, the attribute may be understood to apply only in a general sense or to refer to a significant majority in the group.The word “mga”, which marks plurality, may also appear with it. That “mga”, though, is modifying the noun and not the adjective.The following sentences all mean, “All their children are already grown-ups”. MALALAKÍ* na ang MGA anák nila. Ang MGA anak nila ay MALALAKI na.MGA MALALAKI na ang anak nila. (Some of us might even unnecessarily add another “mga” right before “anak”.)MALALAKI na ang anak nila. (“Malalaki” indicates the plurality, but grammarians may consider the sentence incorrect because of the absence of “mga” either before “malalaki” or “anak”).A Filipino might say, “MATATANGKAD ang MGA Amerikano (Americans are tall)”, and it will be understood only to mean that in general, or based on the average, they are taller. * “Malalaki”, on its own, will have the stress on its last syllable “ki”. But when “na (already)” follows it, we would pronounce it as if “malalaki na” is a single word and place the stress on the “na” instead.The word formation is also used with nouns, but in all cases, the word is applicable to both singular and plural usage. In the following examples, the number of the subject or actors is the basis for knowing if the noun is used in the singular or plural sense. The “mga” may also be added when the noun is used in the plural.Mánanáhî siya. = He/She is a sewer/tailor/dressmaker. (Mga) Mánanáhî sila. = They are sewers/tailors/dressmakers. (Mga) Mánananggól sina Jack at Jill. = Jack and Jill are lawyers. Mandaráyâ ang tindero. = The vendor is a cheater. (The root word is “daya”. We don’t repeat the “da”, but use "ra" for the second “da” instead.)(Mga) Mángingisdâ kami. = We are fishermen.

@Juantutri Thank you for the explanation!
I was surprised because I had not picked up much on this but good to know it's not some malalim na tagalog or something unnecessary.
I've already picked it up more in the podcasts I've been listening to since asking this question!Would you say it's common to intentionally not stress the added part of the root word? Like make sure it's said malalakÍ (quickly saying "malala") as opposed to maLAlakÍ?
And this would maybe help indicate that it's definitely not a verb?

@calinga
The stress is on the same syllable where it would be had the adjective been used in a singular case.For example:
Kapál (thickness) – makapál (thick) – makakapálTalas (sharpness) - matalas (sharp) – matatalasTahimik (silent/quiet) - matahimik (silent/quiet) – matatahimik

Some root words don’t have any stressed syllables. When they become adjectives, the first syllable is usually stressed.Layò (distance) = malayò (far) - malalayòHabà (length) = mahabà (long) – mahahabà The root word of “malalaki” is “lakí (size)” and its singular adjective form is “malakí (big)”, then its plural use can only be “malalakí”.The placement or misplacement of the stress can change the meaning of a word.“Malálaki” is not a proper word, but “malálakihán” means “to find/consider something as big”.Malálakihán si Mary sa damít na ibíbigáy mo sa kaniyá. = Mary will find the dress you’re giving her as rather big. Since “lalaki” is a proper word, if we hear, for example, a word like “malalaki”, we could interpret that as a place largely populated by men. The use of the prefix “ma” there may be thought of as also an abbreviation of “marami (many)” since there are instances when it’s used that way.Malamók sa labás. = There are lots of mosquitoes outside. (malamók = maraming lamók)Mapunò ang/sa lugár nilá. = Trees are abundant in their area. (mapunò = maraming punò)Ang mga lugár na kagáya/gaya ng New York, London, at Berlin ay matao. = Places like New York, London, and Berlin are highly populated. (matao = maraming tao)