Which is better for the imam of a mosque who has no one attending Fajr prayer with him: to pray alone in the mosque, or to pray at home with his family, and does his prayer with his young son remove the sin from those who fail to attend the congregational prayer?

It is best for the appointed Imam to pray in his mosque, even if alone, because he takes the place of the congregation in virtue and ruling, and he receives its reward. He should not repeat his prayer in another congregation, nor is it recommended for him to seek a congregation in another mosque. He is also rewarded for his steps and for raising the adhan (definition). His prayer with his son or anyone else in the mosque does not remove the sin from those who fail to attend the congregational prayer without a valid excuse, whether its obligation is considered individual (ayni) or collective (kifa'i), as the collective obligation requires the presence of a group of free, adult males to manifest the symbol of the congregation.