He stole from his father and brother, and now regrets it
Question

                When I was a teenager, I used to take money from my father and my older brother without their knowledge. Now I regret what I did, and I am wondering whether I should return the money to its owners, but I do not know exactly how much I took.
Praise be to Allah.
    What you did comes under the heading of stealing, but you 
    regret what you have done and the Prophet  (peace and blessings of 
    Allaah be upon him) said: “Regret is repentance.” Narrated by Ahmad, 3558; 
    Ibn Maajah (4252; classed as saheeh by al-Albaani in Saheeh Ibn Maajah. 
    What is meant is that regret is the major part of repentance. 
that you have been guided to repent. Part 
    of your repentance is returning things to their rightful owners, or asking 
    them to forgive you and let you off. 
    
    You have to figure out how much you took, and do your best to 
    work it out, then return it to your father and brother. 

    You do not have to tell them that you had stolen this money 
    from them, rather the point is to return the money to its rightful owners in 
    whatever way possible. 

    See also questions no.
    31234 and
    40157. 

    If you want to tell them what happened and ask for their 
    forgiveness, this will not harm you, in sha Allaah, especially since you did 
    this when you were a teenager and Allaah has now enabled you to repent from 
    it. The Prophet  (peace and blessings of Allaah be upon him) said: “The 
    one who repents is like one who did not sin.” Narrated by Ibn Maajah, 4250; 
    classed as saheeh by al-Albaani in Saheeh Ibn Maajah. 
You must hasten to do 
    that, because the Prophet  (peace and blessings of Allaah be upon him) 
    said to his companions one day: 

    “Do you know who is the one who is bankrupt?” They said: 
    “Among us, the one who is bankrupt is the one who has no dirhams and no 
    goods.” He said: “Rather the one who is bankrupt amongst my ummah is the one 
    who will come on the Day of Resurrection with prayer, fasting and zakaah, 
    but he will come having insulted this one, slandered that one, consumed the 
    wealth of this one, shed the blood of that one and beaten this one, all of 
    whom will be given some of his hasanaat (good deeds), and if his hasanaat 
    run out before the scores have been settled, some of their sins will be 
    taken and thrown onto him, then he will be cast into the Fire.” Narrated by 
    Muslim, 2581. 

    We ask Allaah to accept your repentance, and to help you to say and do the right thing. 

    And Allaah knows best.