@sandhyafern,
You can not save people that do not want to be saved... Although I commend you and what I mean by that is I imagine you are not in India? Therefore the questions..
Is your Mother-in-law telling your husband this, that she suffers when he drinks and if so how? Abuse of words or of physical action? You can advise her of the answers but will he go there?
If your Mother-in-law is suffering from physical abuse when he drinks, she must consider her safety and not be blinded by the word of commitment of marriage until he has seeked help and over come the problem.
People drink through pain, lonliness, un-happiness he is not just an alcoholic, there is an underligning problem..
Apollo Hospitals Group is one of the largest healthcare groups throughout Asia and includes India... But beware of advertising, and find friends in India or join a site in India to confirm what is best.
Ultimately he will not go anywhere unless he wants help
Ultimately your husband should be there for his Mother if the abuse is physical and get her out until it can be sorted.