How can one rectify the error of not informing siblings about the possibility of retrieving university tuition fees after obtaining a scholarship, and is this action considered stealing the father's money?

It is not permissible for a son to take from his father's money without his permission and consent, as long as the father is fulfilling his duty towards his needy son. The son's lying to his brothers is impermissible, and he must repent from it. As for the money the father paid to the son for university fees during his lifetime, if it was a gift to the son to help him during his time abroad, then it belongs to the son. However, if the father paid it for the fees and expenses on the condition that the son return the remainder, then the son must return the remaining amount to his father's estate. If none of this is clear, then the more pious action is to return the money to the father's estate.