If the sin involves the rights of another person then what form should repentance take?
The basis for the answer is the hadeeth of the Prophet (peace and blessings of Allah be upon him) who said: "He upon whom his brother has a right, be it of the nature of money or honor, let him compensate for it before he is made to compensate for it on a day when there will be neither dinar nor dirham to deal with. Instead, if he has a good deed in his account it will be taken away from him and given to the person he had wronged. And if he has no good deeds in his account, sins of the other person will be taken from him and added to his account" (al-Bukhari). Accordingly, the repentant can escape the questioning only by either giving back to the people wronged their due or seeking their forgiveness. If they forgive, he need not worry, but if they do not, then he must return their dues.
And Allah knows best.