Is the inability to complete sexual intercourse a punishment from God for the questioner's act of threatening girls with publishing their pictures, and is giving charity on their behalf sufficient atonement for this sin?

If your repentance is sincere, then what befalls you is not considered a punishment for the sin, for sincere repentance erases sins. However, generally, when calamities strike, the servant should accuse himself and renew his repentance from all sins, for calamities do not descend except due to a sin and are not lifted except through repentance. It is recommended to observe the obligatory duties, avoid disobedience, and increase in remembrance of Allah and supplication.