long distance - Mom refuses to be evaluated & Dad isn't taking action

DDdkd

My parents live in a different city, and we are deeply concerned about my mom’s health. She is 78 and has been showing signs of memory loss for the last couple of years, which are progressively worsening. She refuses to acknowledge the issue, won’t allow herself to be formally diagnosed, and has made my dad promise not to share her struggles with my sister and me. Her mother had dementia, and we suspect she fears the same diagnosis.
She retired just before COVID and was hoping my dad (he’s 80) would do the same. Now, she spends every weekday alone at home while my dad, who runs his own business, is at work. He knows he needs to sell his company but honestly, I don’t think he’s taken any steps to move forward with that decision. He knows that isolation is the worst thing for her and yet...he still goes to work.
Despite having access to a renowned dementia institute and us providing him with a ton of resources from the Alzheimer’s Association, progress is stalled because of my mom’s lack of consent to be evaluated and my dad’s reluctance to take decisive action.
We’ve tried to convince her to come and stay with us even for just a couple of days—offering to pick her up or take the train—but she refuses, providing vague excuses.
Her angry outbursts are becoming more frequent and severe,  and I fear that isolation is only making things worse. We've tried to be direct and have open conversations, but she shuts us out.
This feels like a ticking time bomb. We are worried that if things continue as they are, her mental health will worsen, leading to a potential crisis. I also don’t think they’ve set up any legal safeguards and when we ask about it, my dad brushes us off.
If anyone has advice on what we can do next, especially in terms of how to navigate this challenging situation, I’d really appreciate it. Feeling so incredibly helpless...