Regarding alcohol are all of the three following persons committing a sin: the one who sells it, the one who drinks it and the one who offers it or helps others in drinking but does not drink himself?

We must know that Islam sees a crime and support for carrying it out as equivalent. There is virtually no difference if a person drinks or if he/she sells/serves alcohol to his friends. To my mind, the latter form of the crime is more heinous and despicable since it facilitates the offender to carry out this crime, sets him at ease and makes him comfortable with his crime. It is for this reason that the Holy Qur’ān has warned us not to help each other with evil but what is good and righteous:

Cooperate with each other in matters of piety and obedience; and do not cooperate with others in matters of sin and transgression. (5: 2)

Viewed thus, not only the drinker, but also the seller and the helper in this ‘crime’ commit a sinful act. However, it is very likely that any of them may have been party to the crime due to compelling circumstances. For instance, a person, who is in dire need and has failed to find a job anywhere, may be compelled to work in a bar serving or selling alcohol to others.  In this case, it is hoped that the Ever-Merciful Creator will surely make allowances for the person who is victim of compelling circumstances. He should keep praying to the Lord to help him escape the situation and provide him with an alternative. This prayer and his consciousness of the evil will help him retain his faith and also the desire to tread the right path.