Welcome here, you posted this at 4.47 yesterday, but first posts take a while to be put up, so what appears as us not responding in a timely manner, is actually us not seeing the post until it was approved by a moderator.
We get this sort of question from time to time, and it's a reminder of the pain we ourselves put our own families through when we were drinking, the alcoholic while drinking is selfish in the extreme, we only cared about ourselves, and were blind to the suffering we caused others.
As avaneesh has said the desire must come from her, you have heard the term 'hitting bottom' I expect, and it's at this point she will accept help. It's easy to say but hard for you and your Dad to do, but try not to let this ruin your own happiness and health. The Al-anon meetings were mentioned, and even if you just went to one or two with or without your Dad, it will expose you to others who have been or are in the same situation, they may have advise on how best to handle it, and many have found just going to these meetings improved their own lives in ways they never expected, here is a meeting finder link -http://al-anon.org/find-a-meeting
Bless you for caring about your Mum, and best of luck.
The seed has been planted in his mind. He knows that thousands of men, much like himself, have recovered. B.B. P.113