To whom should a married man should give much preference, either his mother or wife? Praise be to Allaah. The Muslim should always give preference to his mother, because it says in a hadeeth that a man said to the Prophet (peace and blessings of Allaah be upon him): “Who among the people is most deserving of my good company?” He said, “Your mother.” He asked, “Then who?” He said, “Your mother.” He asked, “Then who?” He said, “Your mother.” … (Narrated by al-Bukhaari, 5514; Muslim, 4621). But the wife takes precedence over the mother in one case, and that is the matter of spending. If the husband cannot afford to spend on both his wife and his mother because he is poor, then in this case he should put his wife before his mother. The Muslim has to give what is due to each person who has a right over him, and he has to help the one who is oppressed. If his mother mistreats his wife, he has to put a stop to it, in a kind and fair manner. And Allaah knows best.

I know that smoking cigarets are haram. But what about going to the store and buying them for someone else. And if that is haram too, does that ruling apply buying them for one's father?

Praise be to Allaah. 

It is not permissible for you to buy anything for your father which it is haraam to use, whether it is tobacco, opium, hashish, alcohol or whatever, even if he tells you to do that. It was reported that the Prophet (peace and blessings of Allaah be upon him) said: “There is no obedience to any created being if it involves disobedience of the Creator” and, “Obedience is only with regard to things which are right and good (ma’roof).” You have to advise him and apologize to him politely for not buying them for him.