Curse cast upon a person

I believe that a curse/spell was cast upon my sister to make her stay away from our mother and me, her brother. I am sure that this is all from her husband. He hates us with a passion and it can be seen by his actions and other people have told us. Although, one can tell that my sister has the desire in her heart to stay in contact with her family, there is much that prohibits her in doing so. Her husband also associates with people who practice casting of spells. A few weeks ago, my sister was very sick, vomiting, dizzy and couldn't stand up. She went to doctors and they ran several tests and couldn't find a thing wrong with her. My sister has three children. Two are like in a daze and one child is very hurt that he cannot be with his grandma for long periods of time. This is where I see that my sister still wants to keep a connection. I also believe that there are threats, emotional and verbal abuse in this. There is also a strong hold that there is witchcraft of evil cast upon this situation. Many people of strong Christian beliefs also tell me that it sounds like witchcraft is a key to this problem. Can you please help me with this in some way. I pray daily about it and ask God to open her eyes to what she has before her. Thank you!