The dual refers to exactly two. The masculine example is فَاعِلَانِ and the feminine فَاعِلَتَانِ.
Word / formMeaning / explanation
نَاصِرَانِtwo male helpers.
نَاصِرَتَانِtwo female helpers.
ضَارِبَانِtwo male strikers.
ضَارِبَتَانِtwo female strikers.
Read the whole ending: the dual marker and feminine tāʾ together establish the intended form.