Welsh couple Dom and Kellie weren't fully prepared for the challenges that they would face when their two sons, Lucus and Alexander, were diagnosed with Down's Syndrome and cerebral palsy respectively. Their eldest daughter, Isabella, used to get upset by how frustrated Lucus would become as he struggled to communicate, so she learned Makaton sign language, and it became part of the family's everyday life. 13-year-old Isabella and her brother have now become social media stars - as they share their relationship and teach Makaton to her fifteen thousand YouTube subscribers.