Answer:
The statement by the family that informs the nurse of their understanding of the client's mental illness is "Because of mental illness, my brother cannot think clearly or understand the need for meds".
Explanation:
Many mental diseases require the patient to use their medication correctly, to avoid the attacks that occur by omitting the indicated medical treatment. The same mental condition of a patient predisposes him to abandon the medication.
The fact that the family knows that, because of their mental condition and not thinking clearly, their relative is not taking their medication correctly and is having a crisis, lets the nurse know that they understand the client's illness.