Unless you have guardianship or conservatorship over the parent, you cannot legally take their keys. Until proven incapacitated in a court of law or voluntarily turning over control through a Power of Attorney, they are free to make their own choices, even bad ones....
Caring for an aging parent can be challenging. It is hard to reverse the roles of caregiver and care-receiver. You love them, and making tough decisions that are contrary to their wishes is hard. But just like when they stopped you from playing in the road as a child,...