What should I do to atone for my prayer and their prayers, after I led the people in prayer, and then it became clear that I was in a state of major ritual impurity (janabah)?

Masturbation is forbidden, and one must repent from it. It does not necessitate major ritual impurity (janabah) unless ejaculation occurs. If a person is unsure whether he is in a state of janabah while leading the prayer, his prayer is valid for the congregants, but he must repeat the prayer himself after achieving ritual purity.