Okay, haven't heard back from you about David but I'll go ahead and post census records for the David I mentioned above. You thought David had sons - and he did: David (junior) and Daniel.
This David R Murphy married a Josephine. I don't have their marriage record, but seems safe to say she was Josephine Alexander.
1910 Anniston Ward 1, Calhoun County, Alabama David R Murphy 38, b in Kentucky Josephine Murphy 32, b in Alabama Anne Murphy 8, b abt 1902 in Alabama Josephine Murphy 6, b abt 1904 in Alabama David Murphy 4 b abt 1906 Alabama A C Alexander 56 mother-in-law, born in Alabama John H Alexander 33, married b Alabama Maggie Alexander 23, married b Alabama John C Alexander, six months old, born in Mississippi
1920 Calhoun County, Alabama D R Murphy b abt 1874 in Kentucky Josephine 41 b abt 1879 in Alabama Anne C Murphy 18 b abt 1902 in Alabama Josephine Murphy 16 b abt 1904 in Alabama David R Murphy 13 b abt 1907 in Alabama Daniel F Murphy 10 b abt 1910 in Alabama Anna C. Alexander, 67, mother-in-law, born about 1853 in Alabama
1930 Daphne, Baldwin County, Alabama David R Murphy 55 b abt 1875 in Kentucky Josephine A Murphy 51 b abt 1879 in Alabama Anne C Murphy 27 b abt 1903 in Alabama David R Murphy 23 b abt 1907 in Alabama Daniel H Murphy 21 b abt 1909 in Alabama Anna L. Alexander, 78, widowed, mother-in-law b in Alabama
(1940 census transcription by Ancestry.com says Daniel R Murphy but original handwriting looks like David R Murphy to me)
1940 Daphne, Baldwin Alabama Daniel R. Murphy b abt 1873 KY President, Normal School Josephine, wife, b abt 1878 Alabama, librarian at the normal school
(Normal School = Daphne State Normal College)
1940 - the record below could be David R. Murphy's son David R. Murphy. You had remembered David Murphy as a surgeon living in Florida - so here you go, this matches that memory.
1940 Election Precinct 38, Hillsborough, Florida David R Murphy 33 b abt 1907 Alabama PRIVATE SURGEON Caroline G Murphy 32, b in Tennessee David R. Murphy 7, son b about 1933 in Virginia Bunton R Murphy 2, son born about 1938 in Florida Residence 1935 Charlotteville, Albemarle, Virginia
Thus the most current direct male line descendants are these sons living in 1940 in Florida. I'll also check on Daniel Murphy's whereabouts (Daniel the other son of David R. Murphy).
I won't be able to track people further than the 1940 census - but there are people-search services online that can help.