what does đứa mean?
"Đứa" is colloquial. We don't use it around people we don't know well.
Another acceptable translation: "cô/người con gái," which are more formal.
Yes...i would like to understand this slso..why dua?
another solution: "Anh ta/ Anh ấy có mười hai cô con gái"
There are two of the same answer
I'm assuming it's a coincidence that "con" is used both for one's children and for animals?
Well, "con" means "son or daughter", so as a classifier it seams to apply to things that have sons/daughter, like people, animals, ghosts (they don't have children, but they are creatures) and even rivers or streets (and for some reason, knives).
What does "dua" mean in the context of this sentence?
My lesson had dua but sentence above not.
Where is"đứa "?
Not on above sentence but it was in the actual lesson. Why? Who knows.