How can I get custody of my mentally challenged adult daughters

My ex-husband lives in the UK. I live in the family home in Salt Lake City with my younger son (44 years old) & his family and my daughters. My daughters though 38 are mentally challenged, though the younger girl Renuka is fairly alright. The older girl Radhika has schizophrenia. The twins have been kept totally segregated on the 2nd floor of the building, with no contact with anyone. A caregiver looks after them, appointed by their father. They have always lived with the family, while I worked for my living. I never asked for alimony. I would like custody of the girls, as they are both adults