Is it advisable to marry someone with whom the act of fornication was committed, in order to atone for this sin, especially given the family's rejection of that young man?

It is permissible for a fornicator to marry the person with whom they fornicated if they both repent and mend their ways. The sister must repent to Allah for fornication and leave her mother, and she must mend her relationship with her mother. She must cut off all ties with the young man unless he repents, in which case marriage to him is permissible with the father's consent. If she marries someone else, she should conceal what happened and not inform him. If he asks about virginity, she should tell him that it can be lost due to many causes. Taqwa (definition) (piety, fear of Allah) is the way out of every difficulty, eases every hardship, and atones for sins. Allah says: "And whoever fears Allah - He will make for him a way out" (At-Talaq (definition):2), and "And whoever fears Allah - He will make for him ease in his affair" (At-Talaq:4), and "And whoever fears Allah - He will remove from him his misdeeds and make great for him his reward" (At-Talaq:5).