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

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 many cases of buying antibiotics online 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?