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 'alyhi wa sallam, is His slave and Messenger.
In principle, you should obey your parents and not marry this girl because it is an obligation to be obedient and dutiful to your parents whereas it is not an obligation on you to marry this girl. However, if what you mentioned in the question is true that your parents do not have a sound reason for refusing this marriage except that this girl is from another clan, and that if you do not obey them they will not be harmed with the type which could not be considered as frivolous, then it would be permissible for you –in this case – to marry her, but first, you should endeavour to convince your parents to accept and seek the help of influential people in this regard. However, you should try to please them in any case.
We would like to bring your attention to the following matters:
The Islamic criteria in choosing a spouse are religion and good moral conduct, and social differences should not be taken into account.
You should perform the Istikhaarah [guidance seeking] prayer about this marriage; for more benefit on how to perform the Istikhaarah prayer, please refer to Fatwa 81434.
This girl should be married off by her Muslim guardian, if her father is not a Muslim, then her guardianship is to be transferred to the Muslims who deserve her guardianship according to the order stated by the jurists . For more details, please refer to Fatwa 83338.
If none of them are Muslims, then it is the Muslim ruler or the Muslim community who would marry her off.
Allaah Knows best.