Rule 1: 1. The dual noun in narrative
The dual ends in ـَانِ in the nominative and ـَيْنِ in the genitive and accusative. Its ن drops when the dual is the first term of an iḍāfa or carries a pronoun suffix. Adjectives and predicates agree in the dual too.
اَلْجَدْيَانِ صَغِيرَانِ.
al-jadyāni ṣaghīrāni
The two kids are small.
رَأَيْتُ جَدْيَيْنِ عَلَى لَوْحٍ ضَيِّقٍ.
raʾaytu jadyayni ʿalā lawḥin ḍayyiqin
I saw two kids on a narrow plank.
جَدْيَا الْفَلَّاحِ فِي الْحَقْلِ.
jadya l-fallāḥi fi l-ḥaqli
The farmer's two kids are in the field.
The ن of جَدْيَانِ drops before the second term of the iḍāfa.
وَقَعَ الْجَدْيَانِ فِي الْجَدْوَلِ مِنْ طَرَفَيْهِ.
waqaʿa l-jadyāni fi l-jadwali min ṭarafayhi
The two kids fell into the stream from its two sides.
طَرَفَيْنِ + ـهِ gives طَرَفَيْهِ.