What is the ruling of Islamic law regarding the marriage of a brother who has had two children with a woman he lives with without a marriage contract, knowing that he is recognized for his piety and adherence to religious duties, and how can this problem be addressed?

We are surprised by the ignorance of this brother's parents regarding the prohibition of his relationship with the woman with whom he has children. Adultery is forbidden and is one of the greatest major sins after associating partners with Allah. Allah Almighty says: "And those who do not invoke with Allah another deity or kill the soul which Allah has forbidden [to be killed], except by [legal] right, and do not commit unlawful sexual intercourse. And whoever does that will meet a penalty. The punishment will be doubled for him on the Day of Resurrection, and he will abide therein in humiliation. Except for those who repent, believe and do righteous deeds; for them Allah will change their evil deeds into good ones. And Allah is Forgiving and Merciful." The sin of adultery varies and is magnified according to its contexts, so adultery with a mahram or with a married woman is more grave. One must hasten to repent to Allah, and repentance is not achieved except by completely separating from this woman and severing all ties with her. If he does not respond, then his matter must be referred to whoever is able to change this evil.