Episode #4.5 - S4-E5
Factual error: When Lady Edith visits a Harley Street doctor his nameplate is shown outside his surgery. His name is prefixed with "Dr." However, one of his post-nominal qualifications is "FRCS." As a Fellow of the Royal College of Surgeons, his name should be prefixed with "Mr.", as with all qualified surgeons in the British Isles.
Answer: Lord Sinderby purchased the house, furnished and appointed, from someone else, complete with staff that come with the home (some of whom aren't happy to be working for a Jewish family). He bought the title, as well. If the artwork featuring Jesus is valuable, he might keep it. Also interesting, his ancestors Anglicized their name, though he is proudly Jewish.
Michael Albert