Sibling and husband are alcoholics who traveled from Colorado to northern mn without any money... maxed out credit cards... and no jobs or no place to live. They complain to mom about having no money for food... and professional they want to take care of her. Which would mean just the opposite... she would be shelling out to them. They have no stability in their backgrounds and are looking to her to foot any needs she can give them. How can the current caregiver protect the aging ill? Parent.
If there is no Power of Attorney, get Mom to an Elder Law Attorney immediately to have these legal documents drawn up, as long as Mom can still understand the reason behind having a POA. Also, depending on how old Mom's Will is, it might be time to have that updated in case there are any new State laws.
Now, with a financial Power of Attorney in place, controlling all of Mom's funds, keeping records of bills paid, etc..... then your sister and her husband can't ask Mom for money, they would need to ask the Power of Attorney.
If this turns into a 3-ring circus, the Elder Law Attorney would recommend a CPA to handle the funds, a person who isn't afraid to say no to your sibling and her spouse. But remember, the CPA would be changing an hourly fee to handle the funds.