She committed incest with her brother – should she tell her husband?
Question

                Between the ages of 10 and 14 she committed immoral actions with her brother who was three years older than her, but intercourse did not take place. Then she grew up and realized that she was sinning, and she and her brother gave up this action and regretted it deeply.   

She fell in love with a young man and did everything with him except intercourse. 

Should she tell her husband in the future of what she did with her brother in the past? Is it true that her parents’ marriage is regarded as null and void because of what they did? How should the relationship be between her children and her brother’s children in the future? How can she repent and seek forgiveness for her sins? Will her sin be forgiven if she says “Yaa Ghafoor, yaa Raheem, yaa ‘Afuw” repeatedly?.
Praise be to Allah.What you have to do is to 
    repent to Allaah and seek His forgiveness for what you have done. What you 
    have done is no minor matter. Allaah says (interpretation of the meaning): 
“And come 
    not near to unlawful sex. Verily, it is a Faahishah (i.e. anything that 
    transgresses its limits: a great sin, and an evil way that leads one to hell 
    unless Allaah Forgives him)”
[al-Isra’ 
    17:32]
What you and your brother 
    did is a kind of approaching zina (unlawful sex). Allaah says 
    (interpretation of the meaning): 
“And 
    those who invoke not any other ilaah (god) along with Allaah, nor kill such 
    person as Allaah has forbidden, except for just cause, nor commit illegal 
    sexual intercourse  
    and whoever does this shall receive the punishment.
The 
    torment will be doubled to him on the Day of Resurrection, and he will abide 
    therein in disgrace;
Except 
    those who repent and believe (in Islamic Monotheism), and do righteous 
    deeds; for those, Allaah will change their sins into good deeds, and Allaah 
    is Oft-Forgiving, Most Merciful”

    [al-Furqaan 25:68]
And the 
    Prophet  (peace and blessings of Allaah be upon him) said: “O ummah of 
    Muhammad, by Allaah there is none more indignant than Allaah when His slave, 
    male or female, commits zina. O ummah of Muhammad, if you knew what I know, 
    you would laugh little and weep much.” 
Narrated by 
    al-Bukhaari, 1044; Muslim, 901. 
So what you 
    and your brother have to do is to repent to Allaah from what you have done, 
    and to do a lot of righteous deeds such as praying, fasting and giving 
    charity, so as to atone for your evil actions. 
What 
    happened between you and that man is another sin. Our advice to you is to 
    check yourself and realize that when Allaah becomes angry with His slave He 
    dooms him and removes blessing from his entire life, if he does not repent 
    and turn back to his Lord. 
With regard 
    to telling your husband about what has happened to you in the past, you do 
    not have to do that once you have repented from it. You should cover 
    yourself and not speak openly of something that you have done in the past. 
    The Prophet  (peace and blessings of Allaah be upon him) said: “All of 
    my ummah will be forgiven except those who commit sin blatantly. It is 
    committing sin blatantly if a man does something at night, then in the 
    morning when Allaah has concealed him, he says, ‘O So and so, I did such and 
    such last night,’ when all night his Lord has concealed him, and he uncovers 
    that which Allaah has concealed.” Narrated by al-Bukhaari, 6069; Muslim, 
    2990. 
Your 
    parents’ marriage is not regarded as null and void, because there is not 
    connection between what happened and your parents’ marriage.  
“And no 
    bearer of burdens shall bear another’s burden”
[Faatir 
    35:18]
So if you 
    conceal what you did, and your brother also conceals what he did – which is 
    what you both must do – then the relationship between your children will be 
    very normal and there will be no problems, either from the shar’i or social 
    point of view. 
With regard 
    to repentance from sin and seeking forgiveness for it, there are conditions 
    attached, which are discussed in question no.
    13990. 
May Allaah 
    help you to do all that is good.