Factual error: Marigold can not possibly be as big as she is in this season. She's bigger than George, when she would only be a few months old.
Episode #5.6 - S5-E6
Continuity mistake: When Lady Mary is competing in the Point-to-Point horse race, she is riding her mount sidesaddle style, wearing a long-skirted riding habit. When she (actually the stunt rider) jumps a hedge, she is now riding astride, with both legs over the horse and using a two-stirrup saddle. Also regular riding breeches (pants) are underneath the long skirt when it flies up a bit. These would never be worn with this type of lady's riding habit.
Episode #5.7 - S5-E7
Revealing mistake: When Tom and Sibbie are on the bridge dropping sticks into the water, they run to the other side and you can see their movement through the bricks.
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