Family disagreement and mental health.

I am requesting prayers for peace and understanding amongst my sister, niece and myself.  We are constantly arguing over my niece’s on and off relationship with a boyfriend who is promiscuous, has two children and basically playing on my niece’s attachment to his children. He is very controlling and has recently had a relationship with another woman, which he broke off and is seemingly trying to encourage my niece into getting back together. 
God has removed my niece on two occasions from this man and she doesn’t seem to get it. So I am reaching out to you for prayers for a miracle, that God will take full control of this situation once again and give my niece the wisdom, emotional strength and courage to refrain from getting into any relationship that is not God’s will for her. That God will give her a sense of discernment to recognise the way of His will, and  That God will create a situation where any unfaithful / unhappy relationship would not come to pass. There is so much power when we pray in numbers. 
I also ask you to pray for my sister’s mental health, as she is distraught over my niece’s actions (her daughter), and is burdened with worry that her daughter might make the wrong decisions once again. That there will lasting peace between us all and that we could look back and rejoice at the work of our God Almighty. I pray for urgent intercession of The Holy Spirit in this crisis through Jesus our Lord and Saviour. Amen and thank you for your faithful prayers.