The recent case of Jahi McMath, a 13-year-old declared dead after a routine operation went wrong, raises the issue whether family members can mandate care when their relative is brain dead. The simple answer is No.
In the US, brain death is usually treated conclusively as death. Thus, a family member of a dead person has no right to insist on treatment or to reject the withdrawal of a ventilator keeping the heart and lungs working. Generally, if the evidence is clear, the family need not even be consulted.
While I think it reasonable in some cases for the family to insist on a second opinion on brain death (because doctors can make mistakes), if the facts are clearly established, then the family’s role should be limited to handling the disposition of the body. (I offer no opinion on the strength of the evidence of brain death in McMath, but, a priori, I think it far more likely that the doctors are right than the family.)
Further, comparing brain death in McMath to cases involving coma or a persistent vegetative state (PVS) is not appropriate. People in a PVS or in other forms of comas are alive, while people who are brain-dead are dead.