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 is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The marriage contract of a girl which is conducted without the consent of her guardian is not valid. Details are mentioned in our previous Fataawa: 85026 and 82103.
The father is the guardian of a girl, so, a brother cannot become a guardian unless the father approves it.
You are not allowed to have any relations with the girl before completing the marriage contract. For details read the Fataawa: 81668 and 81356.
We advise you to try your best to convince the father of the girl to marry her off to you. Let him know that marriage does not disturb study; rather it helps spouses concentrate and have the needed peace of mind.
If he does not agree and you are in need of marriage as you mentioned, then we advise you to seek another suitable and religious girl.
Allaah knows best.