Singular forms of demonstrative pronouns are not preceded by Ang mga.
Filipino sentences follow rules in plurality and can be indicated through the subjectorpredicate. By adding Ang mga before the pronoun, it is denoted that it is in plural form.
The adjective of a sentence can be used to express plurality. the adjective's second syllable will be doubled as in "magandá" into magaganda or "malakí" into malalaki. To avoid redundancy, do not add ang mga before the demonstrative pronoun if the adjective in the sentence has already indicated plurality.