Contemporary sociological work has emphasised that family is not static, but actively shaped by ideas of who and what makes family. Disclosure of an illness, including diagnosis of stigmatised infections such as HIV, hepatitis B virus and hepatitis C virus, can change the dynamics of family relationships. This paper draws on 61 qualitative semi-structured interviews conducted between 2017 and 2019 with people in Australia with one or more of these blood-borne viruses (BBVs) and their family members, to understand the experiences of serodiscordant (mixed viral status) families. Through a thematic analysis, we explore the family imaginaries that participants evoked when describing their disclosure practices in relation to (self-defined) family members, revealing how some participants disclosed in ways that enabled them to shape their family, to maintain boundaries between self and family or to protect family from distress. Participants' accounts of disclosure to family revealed imaginaries of family as a precious web of connections to be nurtured or protected, but also as sites of ambivalent belonging and complex history. We conclude that BBV disclosure practices within families reveal important ideas about families that are imagined in response to the threat of loss, change and stigma.