Though there are some very old traditions of magic in your part of the world, there are some things which ring universally true: Nothing can affect a person magically which the person does not allow.
Shielding, cleansing, banishing, binding: These things are all practices which many people put to use.
Your family member may not be under effect of a "madness spell." Keep mundane possibilities in mind as well. A legitimate doctor may have a better explanation, such as mental distress, or a developing condition. There are some mental conditions which may be present genetically, but do not manifest until early adulthood, or due to some sort of physical, chemical, or emotional trauma.