Usually, I would think, if I were rich my sister and brother would also be. Thus, they would appreciate a gift that was more thoughtful and personal than expensive.
Also, in 1907 a car was a hobby, not transportation. Only a very few people would actually want one. Not unlike a Model 1907 Cadillac would be today.
I am giving my sister a book that I really enjoyed and that I would like to share with her. I think she will like that better than a fur coat.
I started this post thinking about what Lord Peter Wimsey would give to Gerald and Mary at Christmas. I doubt if it would (necessarily) be expensive. I can’t imagine it would be fur coats and automobiles–he does give a fur coat to an informant once.