Mom had a stroke last year and Daddy is blind. They can barely take care of what they have now! They should be down-sizing, but they want to buy a brand new house with a huge kitchen. They are not wealthy people, but they have a good middle-class income. Daddy recently bought Mama a new $40,000 car that she cannot drive. She is afraid of it with all of the newer technology. My mother has a pile of health issues and should not drive at all. She has been in a couple of accidents recently. They should be living in a retirement community, but they refuse to down-size. We (three of six children) cut their grass and do all of the upkeep on their home as it is. I help Mama clean, cook, and organize. They are fiercely independent and very stubborn. They think they can pay everyone off. They sit around and do nothing but think of ways to spend their money. If Mama goes out of town without Daddy for a night or two, someone has to come in and take care of Daddy. I understand it is their money and they can do what they want, but what happens when they need nursing care down the road? They have made no plans. Five of us moved in around the clock to take care of them after Mama's stroke. What are these people thinking?
Your plan could be, "Enjoy yourselves, Mom and Dad, and we are always happy to visit you and have you over. But we are not subsidizing you financially." If they can afford a new car and a new house they can obviously afford a lawn service and professional movers and in-home care when Dad is alone. While they are sitting around thinking up ways to spend money, they can add those.
They have control over how they spend their money. All of you have control over how you spend your time.
One other point. If you seriously feel Mom should no longer drive, report her to the dmv. I don't know what happens in your state, but she may be required to take a test to retain her license. This is not about money -- it is about public safety.