Pickle, you can only do what you are allowed to do. And your parents have the freedom to make poor decisions.
I was very much pushed away at a point when my mother started to fail. She would not accept help as "she could manage". She could not and it would have saved months of time if she had, at minimum, allowed me to take over her admin. Sadly it included the period when my father was dying from a brain tumour.
I did what I could, without asking/demanding anything of them. So I used to drive for two and a half hours to pop in for half an hour, as if I was just passing. I had always "already eaten" though had often "bought too much" from an M&S service station, so left some behind. I researched help and then offered to apply for, say, a disabled parking permit. When things were getting too difficult my mother finally allowed me to attend a meeting with the Health Visitor. But she never allowed a panic button, knowledge of where the spare key was kept, or details of any neighbour. She would not tell me when she was going on holiday - difficult given she loved those coach holidays where they pick you up locally and counted you on and off the bus.
Things were bad. But I could not do anything till she had a fall. I worried a lot, indeed each time she did not answer the phone. But finally decided I could only be responsible for things I could be responsible for.
This can be a long haul. Your parents will be experiencing all sorts of weird emotions around fear, powerlessness, feeling threatened etc. They may well play games, get unreasonably angry, and make odd decisions. I don't think you can do much more than be kind and ready to help.
(Other than if things get really bad, gather other family members together for a "family conference", or if you have POA start taking decisions and withstand the emotional fall out.)