What should I do when my 75 yr old father gets abusive both verbally and physically?

I take care of dad 24/7 with help from my son and husband. Today I went off for 4 hours to shop and get out of the house. My son stayed with dad. I had mentioned buying a lift chair from a resale shop while I was out but dad didn't seem interested so I didn't even go look at it. While I was gone he had my son call my brother for him. My brother see's dad twice a month at best.. he told him that he was not cared for here and that he stayed in bed all day (which he does because he refuses to get up unless I insist) stuff like that. My brother told him he was having dinner and would talk to him later. I came home and dad was very agitated. he started abusing me verbally and tried to hit me with his quad cane. I tried to get him to go to his room and calm down. He then tried to get out our front door. He is in a wheelchair and we have 4 steps outside. He would have fallen for sure. he recently received a small check from a nursing home that owed him a refund and he was sure I was out stealing it from his account. His Dr told me most seniors think family members are stealing from them. He wanders around the house at nite and sleeps til noon. he will not stay in bed (at nite)and is constantly ringing his bell and when I come into his room he says he can't remember what he wanted. He also will not tell anyone else what he wants. He says he needs to only tell me. I'm tired and fed up!! Any advice??