Is it permissible for the one getting married to appoint his father or elder brother to act on his behalf in the marriage contract, and is it valid for his father, who does not pray and drinks alcohol, to conduct the marriage contract for him?

The fundamental principle is that appointing an agent for the acceptance of marriage (نكاح) is valid. Therefore, it is permissible to appoint one's brother or father as an agent, even if he does not pray, because it is permissible to appoint a disbeliever as an agent for the acceptance of marriage. Scholars have differed concerning the person who abandons prayer but does not deny its obligation. The majority view is that he is not a disbeliever, while others hold that he is a disbeliever. It is important to advise the father wisely and explain the seriousness of his actions.