While it is helpful to think of ang and ng as articles, because they mark definiteness, they really aren't articles and this could get confusing down the line.
Ang mga is used when we're explicitly marking plurality. Tagalog plurality marking is both optional, and varied. Plurality can be marked with mga, sina/nina, reduplication, and occasionally the ka-root-an affix.
@akosikoneho wow so there's more than one ways to denote plurality 😭. I have noticed the reduplication as you mentioned I guess I'll find out more along the way in my learning progress! Maraming salamat po Sir!
Plural adjectives came as a big surprise to me eg masisipag. I think it only apples to the ma- adjectives but I am a beginner so may be wrong. But French has them too and I think also German. And like the Tagalog sila / nila, English also has him / they.