In this study, we use the contestability exercised by non-dominant large shareholders to measure how internal governance mechanisms influence firm monitoring in a structure with multiple large shareholders. This extends knowledge of principal-principal conflicts and family business by introducing the moderating effects of Chief Executive Officer (CEO) duality and board independence. Using a sample of Malaysian manufacturing family firms, we find that non-dominant large shareholders rely on board independence to strengthen firm monitoring. However, family owners do not utilise CEO duality to weaken the monitoring of non-dominant large shareholders, even though they prioritise firm control to safeguard family interests.