be careful that you don't see this HOUSE as some type of leverage to get him to change. buying a house doesn't get anyone sober. having children doesn't get anyone sober. having an upset spouse doesn't do it i either. also make sure you are not diverting your attention from the BIG problem in your marriage - an active alcoholic husband.
i certainly would NOT recommend making such a large long term financial commitment with someone who is unstable and unreliable.
if your grandparents own the home, is there really an urgency to making a decision THIS WEEK?