You are correct to a point. George only speaks of two children in the actual journal, Jay and Della. His firstborn son, whose name I have as Oscar, was born 10 Nov 1857 and died 4 Jan 1859, just 12 days before Jay was born. Other children were: Glen George, b. 5 May 1865, d. 24 Feb 1944; Clyde Banta, b. 23 Aug 1869, d. 19 Feb 1942; Ralph Laban, b. 15 Nov 1871, d. 5 Mar 1956; Lloyd Elliot, b. 16 Sep 1877, d. 22 Apr 1959.
You have the wrong Lewis Harter. The one who accompanied George and Hanna was the son of George's first cousin, Elam Harter. The final member of the group, Isaac Banta, was Hanna's brother.