We did see David climb out of it.
Yes, and it did look as though the coffin might go onto the floor.
The Coffin is one how many does Barnabas have.
I vaguely remember that in the book
Dracula, the vampire has coffins all over London. Since Willie was making a coffin for Maggie back when she was scheduled to become Josette, it seems fair to imagine that Willie built Barnabas's second coffin. And visited the local fabric shop to get the cloth for the liner.
David has now learned that Sarah is Barnabas' sister, but it Sarah is a ghost what about Barnabas??
Did he learn that? It seems to me that what Barnabas said was vague enough so that one couldn't be sure. I liked how Jason became "the contents" of the mausoleum. David would have assumed that Barnabas was talking about the coffin. By the way, I don't know why Barnabas was contemptuous of Willie's fear. He knows that ghosts exist, and as Jason's murderer, he shouldn't be so certain that he'll never hear from Jason again. On the other hand, I suppose Barnabas has murdered too many people to be worried about one ghost in particular.
Nice job by Alexandra Moltke with the tears, though it did seem strange to hear David turned into a little plaster saint, innocent and virtuous.
I wish they could have shown the secret room of the mausoleum as it really was when the door was shut - pitch black. Imagine being a ten-year-old kid shut in there! The stuff of nightmares for years to come.