The role of the relatives in opt-in systems of postmortal organ procurement

In almost all opt-in systems of postmortal organ procurement, if the deceased has not made a decision about donation, his relatives will be asked to make it. Can this decision power be justified? I consider three possible justifications. (1) We could presume the deceased to have delegated this power to his relatives. (2) It could be argued that, if the deceased has not made a decision, a proxy decision has to be made in his best interests. (3) The relatives could have a standing of their own because they are singled out from the parties whose interests are being affected by the decision by the special relation they had to the deceased. None of these arguments turns out to be convincing.