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.
It was more appropriate for your father to be just between his children, males and females, in gifting them, and he should not have favoured one of them over others, as the Prophet said: “Fear Allaah and be just when gifting your children.” [Al-Bukhari and Muslim] Now that the situation is as you mentioned, the majority of scholars are of the view that you are not obliged to give back to your other brothers what your father gifted you.
However, some scholars are of the view that the son should give back what his father donated to him and this is the predominant opinion closer to the objectives and principles stated in the Quran and Sunnah. Ibn Taymiyyah said: “The person who is favoured over others is not permitted to take what he is gifted, and he should give it back during the life of the transgressor [the one who favoured him], and even after his death.”
Allaah Knows best.