My father has mental issues of his own and is in complete denial regarding my mother's middle-advanced Alzheimer's. What can I do?

Risking her health. My father has been caring for my mother with Alzheimer's for 5 years. He is completely aware of her decline mentally and physically. He has mental issues of his own (mostly depression) but refuses to let us bring in help. He is very selfish and cheap! Recently, my mother had falling episodes. Doctors told us malnutrition most likely caused her weakness and unsteadiness. She now can walk (not well) but, should use a walker ALWAYS. My father doesn't let her use it...says it makes her weaker. He also will not feed her if she says she is not hungry. If you place food in front of her, she will eat like a starving horse. She is no longer capable of performing hygienic needs...showering, dressing, hair, makeup etc.. without assistance. He is not willing to help with any of those needs, yet lies to her doctors and tells them she does it all just fine. He often forgets to give her required medications. When I went to care for my mother after a particularly bad fall due to malnutrition, it was like walking into the haunted mansion. Their home literally had trash, cobwebs everywhere, barely anything in the fridge...but a whole dining table of candy, cookies, donuts, chips. I cannot stay and take care of them indefinitely. I live in California and they live in Oregon. He does not want to hire in home caretakers (housekeepers, food preparation, daily hygiene and memory care). What can I do? He refuses to seek help for his own mental problems. I have added handicap bars throughout the home and prepared the larger bathroom with all the necessary aides. He is also very quick tempered with my sweet mother and says mean things to her. He gets so mad or frustrated that at times I think he would shake her if I wasn't present. I am sooo worried and concerned. I recently had a medical emergency of my own and had to return to California. In my absence, he has admitted to making her stand in the shower that has NO handicap handles and has glass doors by herself while he waited outside the shower. I know for a fact she cannot bathe herself as she thinks she has washed everything before we even begin. He is putting her at risk for yet another fall and doesn't see it! He also admitted to me that his "dinner" for them one night was 2 small, individual snack tray of veggies, cheese, and almonds that I had taken up as "travelling snacks."  This is going to be an endless cycle of malnutrition, unclean house keeping, and poor hygiene. HELP what can I do? I consider this elder abuse of my mother and self abuse for my dad.