With voice user interfaces (VUIs) becoming ubiquitous and speech synthesis technology maturing, it is possible to synthesise voices to resemble our friends and relatives (which we will collectively call ‘kin’) and use them on VUIs. However, designing such interfaces and investigating how the familiarity of kin voices affect user perceptions remain under-explored. Our surveys and interviews with 25 users revealed that VUIs using kin voices were perceived as more engaging, persuasive and safer yet eerier than VUIs using common virtual assistant voices. We then developed a technology probe, KinVoice, an Alexa-based VUI that was deployed in three households over two weeks. Users set reminders using KinVoice, which in turn, gave the reminders in synthesised kin voices. This was to explore users' needs, uncover challenges involved and inspire new applications. We discuss design guidelines for integrating familiar kin voices into VUIs, applications that benefit from its usage, and implications for balancing voice realism and usability with security and diversification.