Since Prince Augustus Frederick had no legitimate children, the title Duke of Sussex became extinct when he died in 1843. The title was revived in 2018 for Prince Harry when he married Meghan Markle.
Prince Albert tells one of Victoria's paternal uncles that they are related. They don't specify how, but Queen Victoria's great Grandmother (the mother of her grandfather George III) was the sister of one of Alberta grandparents.
The concern about a Catholic as head of state is that he / she would be pledged to obey the Pope, theoretically giving the Catholic church ultimate control. This same concern was also a debated issue in the 1960 presidential election in the U.S. Although John F. Kennedy won, it was by a only very narrow margin, which was largely due to the catholic issue.
The number of viewers increased slightly to 5,773,000 for the fifth edition of Victoria, moving the show up one place to eighth in the ITV rankings for the period 12th - 18th September 2016.