You are right as both nicotine and alcohol dependence have significant effect on mental health. His irritability could be independent or also be a part of depressive symptoms. Kindly seek psychiatric consultation, so that a thorough assessment can be done. Deaddiction can be done with anticraving medications and nicotine replacement therapy along with regular counseling. A physical examination will also be required to assess the extent of physical ill effects of the substances and can be used as a motivating factor for deaddiction. Hope this helps, good luck.