Does a girl bear the sin of her husband's wife and children after marriage, and is a man's fear of his wife related to punishment from Allah, knowing that she feels at ease after prayer and supplication?

A man marrying another woman is not an injustice to his first wife, nor is he required to inform her or seek her permission. Rather, what is obligatory is to be just between them in terms of lodging, maintenance, and clothing. There is no objection to you marrying this man if he is of good character and religious, provided that the শরীʿআ (Islamic law) conditions for marriage are met, that you consult your family, and that you perform Istikhara (prayer for guidance). If you know that your marriage will lead to the displacement of his family, then it is preferable to advise him to pause and preserve his family. It must be emphasized that the relationship between a man and a woman before marriage is impermissible, and that it is important for a Muslim to be keen on residing in Muslim countries.