Praise be to Allah.
Note that is is impossible for things to stay the same forever. Glory be to the One Who changes His slaves’ circumstances and directs them as He wills. Our advice to you concerning this problem is first to think of marrying the relative whom your father has suggested that you marry, regardless of the previous knowledge to which you refer. If she more or less has the qualities that you want in a righteous wife and she does not have any bad quality that you think you could not put up with, then marry her. Perhaps Allaah will decree much good for you in that, and your honouring your father will be the cause of happiness in your marriage.
But if there is an obvious fault that means that you could not marry her, then explain that to your father and try to convince him that forcing a man to choose a wife whom he does not like could cause the marriage to fail and could also cause harm to that girl. Advise your brothers to try to honour your father and keep in touch with him so as to strengthen the family ties and put right what has changed. And Allaah is the Source of strength.