«جَاءَ اللَّذَانِ نَجَحَا» — The two who succeeded came.
«رَأَيْتُ اللَّذَيْنِ نَجَحَا» — I saw the two who succeeded.
The relative is respectively a nominative subject marked by alif and an accusative object marked by yāʾ.
The dual subject suffix of «نَجَحَا» supplies the ʿāʾid.
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Relative Nouns — Ṣilah, ʿĀʾid, Forms and Syntax
«جَاءَ اللَّذَانِ نَجَحَا» — The two who succeeded came.
«رَأَيْتُ اللَّذَيْنِ نَجَحَا» — I saw the two who succeeded.
The relative is respectively a nominative subject marked by alif and an accusative object marked by yāʾ.
The dual subject suffix of «نَجَحَا» supplies the ʿāʾid.