I rather doubt Bix's family engaged C.H. Murphy. By 1921, Murphy was regarded as “an old friend of the Palmers” (F.W. Elliott, “My Impressions of D.D. Palmer,” in B.J. Palmer, Fight to Climb (Davenport, IA: Palmer School of Chiropractic, 1950) p. 50). When D.D. Palmer died in 1913, Murphy spoke at his funeral as one of those who knew him “most intimately” (Fountain Head News (2:1). When a large memorial bust of D.D. Palmer was unveiled at a convention of the Universal Chiropractors’ Association in August 1921, Murphy gave the principal address at the dedicatory exercises (Coscannon once noted this here).
It’s not impossible that he acted as Bix’s attorney, but my guess is that, being close to the Palmers and Davenport’s chiropractic circle, Murphy was brought in to consult on behalf of Preston Ivens and his daughter, perhaps to explain the legal dimension. (Having once served in the County Attorney’s office, Murphy would have had valuable insight.) All of the others whom Ivens is known to have consulted—-B.J. Palmer, Frank W. Elliott, and John H. Craven—-were deeply involved with the Palmer School (Ivens testimony). Palmer was head of the School; Elliott its Business Manager; Craven, among other things, the School chaplain. (Rolf E. Peters and Mary Ann Chance, “The Palmer School of Chiropractic: Development of the Faculty 1906-1945,” Chiropractic Journal of Australia, vol. 33, no. 3 (September 2003): 98-116.) Thus, Ivens’ consultants were collectively capable of providing financial, spiritual, and legal advice.
Please note that while I can't be sure of the above, it's not quite speculation. I'd call it an inference partly grounded in the facts I've noted, partly in my legal instinct that in acting for Bix, Palmer would have found himself in at least a situational conflict, given his closeness to the Palmers.