Demonstratives: Dual and Plural

For two people or things the demonstrative takes the dual and, unlike هذا and هذه, it changes with the case:

• masculine: هذان as the subject, هذين after a verb or a preposition
• feminine: هاتان as the subject, هاتين after a verb or a preposition

The noun takes the matching ending: هذان الكتابان مفيدان (These two books are useful), but قرأت هذين الكتابين (I read these two books) and في هاتين المدينتين (in these two cities).
Tip: the ending -ان goes with هذان / هاتان, the ending -ين with هذين / هاتين.
For a plural of people, men or women, use هؤلاء. It never changes: هؤلاء الرجال أطباء (These men are doctors), رأيت هؤلاء الأطفال (I saw these children).