How can I prevent my wife or her parents/ family from taking my children and filing for custody? We are not separated/Divorced- she is mentally ill.

My wife has several medical/mental disorders:Borderline Personality Disorder, Major Depression (suicidal), severe anxiety, uncontrolled seizures and PTSD for which she has been hospitalizied 4 times in 6 months. She is currently unable to drive and has a male "supporter", that is also mentally ill, driving her around and staying with her. She moved out September 2010 and took the children against my wishes (ages 6, 8, 10). Each time she goes into the hospital I care for the children 24/7. she has been in the hospital three times since March- six weeks total. Her behavior has been increasingly more self destructive including substance abuse (seeking or using), driving while suspended with children+driving off the road, assaulted patient while in mental treatment facility, adultery (confirmed by boyfriend), suicide attempts x 2 (Temporary detention order issued last week) and overall poor life choices without accountability. She gave her father a power of attorney.