Any tips on discussing bill paying with father who has dementia?

Really, selling his house while he is still alive will save you a ton of grief down the road. Once my dad's bank got the shot of money from the sale of his house, the return of his investments did much better (his "money making machine" worked better with a higher balance.

OMG 😱 I just love this.... every month she builds up her credit balance, even tho statements probably read Credit Balance No Payment Necessary. Lol. I bet your mom has always been quite the precise person for “bookkeeping” and ran a wellordered household. It’s so especially sad for those that are like this (my late mom was but on the flip side my DMIL was beyond a financial terrorist) when dementia sets in as they seem to intuitively know they things are going amiss and it scares the crap out of them & they become way way fearful atop the usual dementia paranoia.

on the plus side, usually once the $ hits a certain tipping point, the creditor should send her a check to zero out the account.

Good idea of having durable poa. That is what my brothers have. I am now her medical representative.

"That person will need copies of the documentation to share with every entity your Dad has/is doing business with."
Not necessarily - while I did need the POA for some, most "billers", such as utilities, newspaper, phone, etc, didn't care. Most of them I called and provided the account name/number and requested a billing address change. They don't care where the bill goes, they only care about getting paid. I did NOT add my name to any accounts (two of us were already on mom's credit union account.) The town water dept even ASKED me if I wanted the bill mailed to me without me asking first (called to check on the balance due, as the bill was MIA.)

If OP can snag the bills, even older ones, just to have the contact information, then a simple call to most with a request to change the billing address should work. As with others who have dementia, if it doesn't show up in the mail, they will likely not remember that they should be getting it! Best first step is the POA paperwork. Second step should be the bank(s) he uses. From there it would be billers and CC. With CC, if you choose to let him keep it for now, check the available limit and have them reduce it considerably! Mom's was good credit, good payments, so her limit was some ridiculous double digit amount - ripe for abuse if card is lost, stolen or he gets talked into giving the number/date/CCV out! Next would be to consider taking over SS as rep payee and same for any other income he has (this was the only way I could get access/have documents sent to me.)

The only entities who required the POA were the credit union, the bank, and mom's credit card. That last one was the biggest PITA! They gave limited access and denied any online access. At some point I froze the account and then closed it.

It might not be the same everywhere, but not one biller (other than CU, bank and CC) ever asked me who what when where or why. I also avoid autopay - there are too many of my own accounts and mom's to juggle all that - I find have paper statements easier. Then there's always a chance of an oops on their side, resulting in taking too much! It is easier for me to have the paper trail handy if I ever need it! I DO use the billpay system, but it only requires set up once and then just schedule date and amount of payments. Push rather than allowing them to pull.