I know I dont have all the facts of this rather large family of speaker companies,so Jan,John A.,and Frank correct me if I dont get it all which I know I wont.
Rogers
Spendor Harbeth
Epos
So fill in the blanks for me I havent forget Kef,and Sterling,but I dont know where they fit at in the family tree of companies and designers.
You're beginning at the wrong end. Most of the companies, and the various offspring from the companies mentioned, originally came from the BBC after the second world war. As the engineers gained experience and felt they could be financially successful on their own, they eventually broke away from the BBC group to design and often build their own product. Some few companies such as KEF and Celestion were always speaker manufacturers. To my knowledge Quad was always Quad. Peter Walker began the company before the war, but really gained his fame after the war ended.
I don't know that there is a family tree for the rather !ncestuous lot from England. It would be similar to tracking the history of the Boston/Cambridge companies here in the US through the 1950's, '60's and '70's.
There are several biographies and histories of the British audio world after the war if you would care to go through them. Otherwise, companies such as Sterling and Epos are considered Johnny-come-lately's when you are speaking of the Golden Age of British Audio.
And Robin Marshall what role did he play at BBC? Because his pholosophy seems quite a bit different although I do see a few of the genes.His design of Epos seems more in line with Celestion,than the guys he worked with at BBC and the rest went on to form Harbeth and Spendor.The Wway I gather it he stayed with BBC or was he at Rogers all the way until 1981.