Complex sentence: "Sanguinarium" was such a case, being written by sisters Vivian Mayhew and Valerie Mayhew, a duo having their first experience with writing an one-hour network program, who would later be responsible for several episodes in the series "Charmed".
Split into simpler sentences: Sanguinarium was such a case, being written by sisters Vivian Mayhew and Valerie Mayhew, their first experience with writing an one-hour network program. They would later be responsible for several episodes in the television series "Charmed".