It is unusual to hear voices and to see ghosts. You also described your husband as “walk [ing] around like he is just not really there anymore.” That behavior might be indicative of depression or possibly the early phase of a psychotic disorder. Based on limited details it is difficult to determine what may be wrong.
If he is experiencing psychosis (which is associated with schizophrenia and other psychotic disorders), then it is imperative that he seek treatment immediately. Psychosis requires intervention and if left untreated, it typically becomes worse. If safety issues are a concern, then contact your local mental health crisis team. The team can visit the home and conduct an onsite evaluation.
Be vocal about your concerns. Encourage him to have a psychiatric evaluation. If you are willing and if you think it would be beneficial, offer to attend the evaluation with him. It would send him the message that you care about his well-being and might increase the likelihood that he would be open to treatment. If he is unresponsive to your attempts to help him, then you may want to involve friends or family members who you believe might help.
If you have additional questions, please don’t hesitate to write again. Please take care.