Dad is trying to be my dying mom's caregiver. But he is mentally unable to and won't admit. Help!

Mom is in home hospice care. Dad is trying to be her caregiver, but he is mentally unable to and won't admit. Help! My mom is dying and very worried knowing that my father is unable to remember details, and do basic care for himself let alone her. He has forbidden me to speak with the rns, and we are very frightened by the thought of him controlling her medicine and end of life decisions. Any ideas on how to handle this situation? Mom has spent her life trying to not make him angry and wants to die in peace, but my only concern is her comfort.