Scam protection advice?

Credit cards should now be cancelled and you should have sole control of the accounts. This is difficult to do from across the country. It is also IMPOSSIBLE to do with a POA for, as a POA you act for them, at their direction , to do as they tell you to do. You say that they are on a fixed income and live below the poverty line. At this point, then, it is far to late. You can look at this pile of receipts that total up to 4,000.00 and understand that it would buy the TWO of them not even ONE month in Assisted Living.
Quite honestly, without guardianship, there is very little you can do. They will eventually, if they live so long be in a nursing home that provides care for Medicaid payments. The fact that they may have been scammed for say 30,000 over time, while it is sad and awful, would not have bought the two of them a whole lot more than 4 months in assisted living.
It is what it is. You can fight now to get guardianship and control, to become Rep. Payee for Social Security. This would give you a lot of cost and a lot of work would be the result. My brother ASKED me to become Trustee of his Trust when he got a diagnosis of probable early Lewys. It was a tremendous amount of work to get everything ironed out with all entities from supplemental insurance to banks. Meticulous records must be kept, and more so if you are Representative Payee. I gave him his own charge card which I paid and oversaw, and his own spending account, which, careful guy that he always was he actually GREW over a years time. But it will still a lot of work, and it was hard to do from another town.
I couldn't wish you more luck. But if they have no money then this will be self limiting, and if this is their habit it won't stop now. They have living thinking gambling can win you something. It is likely how they will die with what little is left of spending money. At least they aren't giving the money away in chunks to some ungrateful grandkid, as that would count as gifting and go against them in a bid for medicaid. The best thing you can do now is to prepair all accounts and stuff you can for the 5 year (or less in some states) lookback for medicaid.

If you become representative payee for their social security they will not be able to have any access to their money.

If you can't stop them from doing ludicrous things then that may be your only option.

Have you tried prepaid debit cards that once they blow that weeks or months allowance they don't have any money until next month?

Have you taken away their credit cards?

How do they feel about giving up control of most their finances? My parents are dead set against it, so I had to decide that I can't do anything and that includes bailing them out financially.

Read your profile, curious are you moving across the country to be near all these elders or get away from them? Upending your life to move close by will not end well, I can almost say for certain.