The Virginia State Bar has a website with information on this issue: http://www.vsb.org/site/publications/health-care-decision-making-what-you-need-to-know/.

I am not licensed in Virginia, but I can give you a general answer to your question. Who can serve as a surrogate decision-maker is governed typically by state statutes. In Texas, for example, if someone is unable to make their own health care decisions due to incompetency or being a minor, we have statutes that specificy who may authorize (or decline) health care. If, however, the incapacitated person has given a health care power of attorney (POA) naming a specific person as authorized to make those decisions, then the person named in the POA will have the authority rather than the individuals in the statute. So for example, assume I am married but I gave my brother a health care POA. If I'm in the hospital and unable to make my own health care decisions, then my brother gets to make all the decisions not my husband. If there were no POA, then my husband would make the decisions. Also, note that in Texas, a court-appointed guardian who has been given authority to make health care decisions will trump someone named in a POA. So if my husband disagreed with decisions made by my brother, he could file a guardianship action in court to try to get control.

As I understand it, some states do not have statutorily authorized health care decision-makers, so if there is no health care POA then I suppose one has to go to court to be appointed as the guardian in order to make any decisions.