Can you specify in my living will who I don’t want making medical decisions for me?

There was a recent question about family arguing about putting someone in a nursing home.
The question is, to whom does the medical staff listen? They do not know the family dynamics and history, and they don’t know which relatives don’t really have the patient’s best interest in mind. There are where can i buy prescription drugs without a prescription many cases of adult children being estranged for years, but if they show up when the parent is ill, there is the danger that hospital staff will listen to them. So, can a living will prevent them from having a say?