http://www.myjacobfamily.com/favershamjacobs/sydneylongjacob.htm has some information on him.
This recollection by Col. Jacob's son Alexis of his sister includes some brief biographical details of Col. Jacob.
Peter Conlan's article, ' "What are you doing for Christ in Birmingham?" The History, Strategy, and Legacy of a Missional Brethren Assembly Founded by Alexis Jacob in 1924' is a chapter in Neil Dickson, T.J. Marinello [eds], The Brethren and the Church, (Glasgow: BAHN, 2020) pp.217-227, and contains quite a bit of information about the Jacob family, including Sydney Long Jacob.
Timothy Stunt
Philip
STEM publishing has a little biographical outline of the colonel, some of his writings and a preface by your grandfather, A. Jacob, at: https://www.stempublishing.com/authors/Jacob/index.html.
