Undoubtedly alcohol is haraam and is a major sin. Allaah says (interpretation of the meaning):
“O you who believe! Intoxicants (all kinds of alcoholic drinks), and gambling, and Al‑Ansaab [stone altars for sacrifices to idols, jinn, etc], and Al‑Azlaam (arrows for seeking luck or decision) are an abomination of Shaytaan’s (Satan’s) handiwork. So avoid (strictly all) that (abomination) in order that you may be successful.
Shaytaan (Satan) wants only to excite enmity and hatred between you with intoxicants (alcoholic drinks) and gambling, and hinder you from the remembrance of Allaah and from As‑Salaah (the prayer). So, will you not then abstain?”
It was narrated that Anas ibn Maalik said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) cursed ten people in connection with alcohol: the one who presses [the grapes, etc], the one for whom that is done, the one who drinks it, the one who carries it, the one to whom it is carried, the one who pours it, the one who sells it, the one who consumes its price, the one who buys it, and the one for whom it is bought.”
(Narrated by al-Tirmidhi, 1259; Ibn Maajah, 3381. Classed as saheeh by Shaykh al-Albaani in Saheeh al-Tirmidhi, no. 1041).
It is not permissible for your husband to speak in this manner. This is not the response of a Muslim who must accept as forbidden that which Allaah has forbidden. It is not permissible for him to put obedience to his brother above obedience to Allaah, or to anger Allaah by pleasing his brother. If he adheres to the commands of Allaah, Allaah will protect him from his brother, but if he angers Allaah by giving precedence to pleasing his brother, Allaah will leave him to his brother. It was narrated from ‘Aa’ishah (may Allaah be pleased with her) that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Whoever pleases Allaah by angering the people, Allaah will be sufficient for him. But whoever angers Allaah by pleasing the people, Allaah will leave him to the people.”
(Narrated by Ibn Hibbaan in his Saheeh, 1/115; classed as saheeh by Shaykh al-Albaani in al-Silsilah al-Saheehah, 2311)
He can tell everyone – not just his brother – “No, this action is haraam.”
Socializing with them for work purposes does not justify drinking alcohol. His saying that he is not doing anything wrong is very strange indeed. What does he call his drinking? Can we expect that his socializing with his brother and his friends does not involve anything other than alcohol? It is well known that such people will have women with them, and they will listen to music and ignore the prayers. All of these are major sins.
You have to persist in advising him, keep on doing so and do not get tired of it. Look for someone whose advice will have an effect on him.
Make a lot of du’aa’ asking that he be guided. We ask Allaah to guide us all to that which He loves and which pleases Him.
And Allaah knows best.