Complex sentence: His father was Thomas Matthews Rooke, for many years Edward Burne-Jones' studio assistant, and an accomplished artist in his own right; his mother Leonora Rooke (née Jones), who had been governess to Burne-Jones daughter, Margaret.
Split into simpler sentences: His father was Thomas Matthews Rooke, for many years the studio assistant of Edward Burne-Jones, and an accomplished artist in his own right. His mother Leonora Rooke (née Jones) had been governess to Burne-Jones's daughter, Margaret.