الطَّالِبَانِ أَفْضَلُ طَالِبَيْنِ.
With indefinite iḍāfah, the elative stays singular masculine; the indefinite complement fits the compared subject in number and gender.
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Indefinite Iḍāfah: The Important Qualification
Ism al-Tafḍīl: Formation, Comparison, Agreement and Parsing
الطَّالِبَانِ أَفْضَلُ طَالِبَيْنِ.
With indefinite iḍāfah, the elative stays singular masculine; the indefinite complement fits the compared subject in number and gender.