Can a family member decide a patient's care without power of attorney?

Yes. If the patient is incapacitated, then a family member is authorized to make healthcare decisions according to that state's specific laws (e.g. Parent then any child vs eldest child). If a poa has previously been assigned & legal papers properly completed, then that poa has legal right to make healthcare decisions. However, any surrogate gets to make healthcare decisions only if the patient can't.