Feminine dual

Demonstratives — forms, syntax and usage

وَ«تَانِ» وَ«تَيْنِ» لِمُثَنَّاهُ.
Translation: The feminine dual uses tāni and tayni.

هَاتَانِ is nominative; هَاتَيْنِ is accusative or genitive. Compare «هَاتَانِ طَالِبَتَانِ» with «رَأَيْتُ هَاتَيْنِ الطَّالِبَتَيْنِ».