All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The guardian has no right to reject someone who proposes to marry a girl under his guardianship if such a man's religiosity and moral conduct are satisfactory; we have already clarified this in Fatwa 87621.
The fact that your father does not like this young man's father, or that dissension exists between your cousins and his father does not justify rejecting his proposal. Therefore, we advise you to invoke Allaah in prayer, and to be kind with your father and try to convince him even by seeking the help of some righteous people who you think he would listen to.
If he is not convinced, you have the right to take the matter to an Islamic court to marry you off if your father insists on refusing.
However, if you prefer to satisfy your father, then it is up to you, and Allaah may bless you with someone better than this young man because of this.
Allaah Knows best.