Try to convey your worries and concerns in a loving and non-confrontational way. Try to remain calm, focused and respectful. Remember, although the eating disorder may be tearing your family apart, your loved one did not choose to have it. Eating disorders are serious mental health conditions.
Blaming them or listing all the terrible things that are caused by the eating disorder is not going to make them feel good about themselves. They are more than likely already suffering from low self-esteem, and hearing negative things like that are only going to make them feel worse about themselves, and cling to the eating disorder even more.