“The mother’s argument throughout the appeal process relies heavily on the concept that this information is not relevant to anything other than the father’s knowledge of the mother’s HIV status, i.e., it is argued that it has no impact on any welfare decision to be made in relation to the children. This is not agreed on behalf of the children’s guardian and it is submitted that the issue of the mother’s HIV status is a fundamental part of the case in both the context of welfare and threshold.”