How to help a parent with dementia?

I had a step-FIL with Parkinsons who was resistant just like your dad, but was happy to have us orbit around him -- just totally unwilling to trust us with PoA or see into his finances and in denial about his future. We knew he was broke (he never really worked, and borrowed money from everyone and never paid them back) so I got the Medicaid app and started to help him fill it out, but when he got to the end of the app and understood that the state would take his SS he wouldn't sign the app. The only thing left to do was to inform him of the reality of his choice: we weren't going to continue orbiting around him (we couldn't for many reasons). He wasn't going to "recover" from Parkinsons, he'd only get worse and eventually need a facility. If he wanted us to continue to help him he'd need to assign us as PoA. If he didn't, we'd call APS when things got bad enough and he'd become a ward of the county. He didn't, and he became a ward of the county eventually dying alone in a crappy county facility. We laid out the reality of his choices. He chose distrust. I'm sorry to say you will need to do this with your dad but him having reality explained to him will likely not change his mind.

I have to ask if he is an alcoholic? Just put up boundaries to protect yourself and keep then up. I wish you peace in your heart whatever he chooses.

First off, your father needs to appoint one of you as his medical and durable POA, before his dementia gets any worse, because otherwise the state will have control over him and his affairs, unless you apply for guardianship, which costs thousands of dollars. Secondly, if your dad is having seizures, drinking alcohol is the worst thing he can do, as that will override any seizure medications he's on, which in turn will trigger his seizures. My husband after his stroke, developed seizures, and early on he occasionally liked to have 1 beer in the evening, and guaranteed, just like clock work, the next morning he would have seizures. So we learned the hard way that he could never drink alcohol again.
If your father isn't going to listen to you or any of his children, then you may have to report him to APS, and let them figure out the best and next course of action. There are no easy answers. Wishing you the best.