At the time of the sinking, the two most famous passengers aboard the 'Titanic' were actually Lady Duff Gordon and William T. Stead. Had they missed the boat, they would still be remembered and written about today.
Lucile is best served by our very own Randy Bryan Bigham - when his biography finally makes it to print (and it is long over-due!), it will certainly be the seminal work on her life, times and career. 'The It Girls' by Meredith Etherington-Smith and Jeremy Pilcher is a dual biography of Lucy and her sister, the novelist Elinor Glyn, and is extremely well-written and informative, although I feel that Glyn is awarded coverage at Lucy's expense. There are several other books on Glyn herself and these might come in handy when trying to obtain details about the Sutherland family and the sisters' relationship to one another. Lucy's own memoirs, 'Discretions and Indiscretions', are truly enchanting but it is now hard to find a cheap copy on sale. I read them at the Bod in Oxford but I've never seen them elsewhere - and not for want of looking!
Be that as it may, in recent years Lucile has received greater attention and acclaim from costume historians and resumes of her career can be found in any good book on period fashion and society.
It occurs to me that Randy has already published a life of Dorothy Gibson, entitled 'Finding Dorothy', which looks wonderful, although I think that it may have had a limited print run.
A biography of Stead (called, I believe, 'Stead: The Man') was published - possibly privately - in 1914. I'd need to check the name of the author but it is cited by Don Lynch in the bibliography to his 'Illustrated History'. Stead also gets quite a lot of coverage in Barbara Tuchman's superb 'Proud Tower' which can be easily obtained second-hand on Amazon or in libraries. And not so long ago, I came across a compilation of articles actually WRITTEN by Stead in the 1890s and 1900s - I seem to recall that they were a series of profiles of the 'great men' of that time. Any serious work dealing with prostitution or social reform in the late Victorian Era will undoubtedly reference Stead and his crusading work in those areas. There was even a Channel 4 documentary devoted solely to Stead about four years ago!
Benjamin Guggenheim's daughter, Peggy, was a legendary figure on the twentieth-century arts scene in both Europe and the States and many biographies have been written about her. Information on her parentage and early life can naturally be found in any of them. If memory serves, there is also a book called 'The Guggenheims: An American Epic' which chronicles of the history of this exceptional family.
Back in 1912, the Astors were the American equivalent of royalty, proverbial for their wealth and grandeur, and numerous books have been published about them. Just have a root around in your local library or second-hand book shop. The Colonel was a fascinating figure in his own right but his mother, THE Mrs Astor, was a social giantess and she tended to dwarf all her descendants!
The Wideners would surely feature in books about the super-rich of the Gilded Age, particularly in their hometown, Philadelphia. Presumably, these are far easier to obtain on the other side of the pond than here in England. I'm not aware of any specific titles but there MUST be books about American tennis, which might reference Karl Behr, and also about the history of shopping and retail, which would chronicle the career of Isidor Straus at Macy's.