احْتَجِبَا مِنْهُ
“You two should cover yourselves from him.”
احْتَجِبَا is a command addressed to two people; the final ا signals the dual form.
أَفَعَمْيَاوَانِ أَنْتُمَا؟ أَلَسْتُمَا تُبْصِرَانِهِ؟
“Are you two blind? Do you not see him?”
أَنْتُمَا means “you two.” تُبْصِرَانِ is likewise addressed to two people, while the final هُ refers to Ibn Umm Maktum. The questions bring their own capacity to see into focus.