How do I help my mom?

My mom is 67 years old and has been having some memory loss for awhile now (i.e. forgetting children's birthdays, recipes). Over the last year she has been progressively more paranoid. She thinks my dad has been rearranging her stuff and hiding stuff from her. I didn't think much of it since I thought normal aging would cause lack of remembering birth dates and she has always been a bit paranoid about people touching her stuff. Since I was a child, she has always kept her pocketbook right next to her even going as far as sitting on it. In the past month, everything has gotten way worse. She started thinking that her next door neighbors are fighting at night and that the husband is abusing the wife. She tells these elaborate tales of him making his wife dig medication out of the ground and the girl running down the street screaming. I know none of this is true because I live across the street from my mom. That has progressed within a month to her believing the man is saying her name and is going to burn down her house. In the past 2 weeks, she has started having more hallucinations. She calls me every night around 10pm saying that people are outside. The other night she thought someone was trying to steal their truck. Last night, she thought my brothers ex-wife was outside saying that my nephew had died. She even asked me if he was dead today. My brother called saying she was talking to a woman through the vent today as well. When I asked her about it, she said it was the woman next door. I asked her what she said. She told me that she said she was from my mom's childhood neighborhood and that she has a child by my dad. I have tried to convince her to go to the doctor, but she says she doesn't have the money. I have offered to pay for the visit, but she makes other excuses. I have begged her to let me go to the doctor with her when she has her regular checkups, but she won't. My father will not listen to reasoning and help me out. He just says she's a liar or says he will tell the doctor, but never does. My brothers have issues with drug abuse and are in and out of jail, so there is no real help there. The only reason my brother told me about the vent talking today was because he was afraid my dad was going to throw him out and he needed a place to stay. So, here I am, asking for help. I don't know what to do. Today she barely even seemed to know she was talking to me and only wanted to talk about the woman in the vent. She has had issues with pain pill addictions in the past, but has never had issues like these arise with them. She recently had an issue with really low potassium and had to take pills for it. Maybe she is having that issue again? Maybe it is dementia? Lord, I hope not. I love her so much and don't want her to go through anymore pain in her life than she already has. How do I help her if she won't let me go to the doctor with her? Could this be something besides dementia? Thank you for taking the time to read this. Any help would be appreciated.