In regard to your query about Daniel Losh and his wife Elizabeth Jackson, I do not have any documentation on their marriage and I haven't found anything on the David Losh, (son of William Losh), that you mentioned who married Effie Helmick, but I will keep checking and let you know if I find anything.
According to an article from the Sunday Exponent-Telegram dated June 12, 1932, entitled "Doddridge Woman to Celebrate Hundredth Birthday Tuesday", the subject of the article, Mrs. Sarah Margaret Curry of Doddridge County WV, was the daughter of David and Elizabeth (Smallwood) Losh. She was born June 14, 1832, in Dayton, Rockingham County, Virginia. Her paternal grandfather, Daniel Losh, came to America at an early date from Germany, where he was born. He married Elizabeth Jackson and they located in Rockingham County, Virginia. The article lists the other children of Daniel and Elizabeth (Jackson) Losh as follows: Andrew Losh, who lived and died in Rockingham County, Virginia; William Losh who married a woman named Kephert and lived and died in Lewis County, WV; Joseph Losh, who remained single and died near Avon in Doddridge County, WV; Mary Ann Losh, who did not marry and also died in Doddridge County, WV; and Mariah Losh, who married a man named Shaffer and lived and died near Avon in Doddridge County, WV.
The article goes on to list the sons and daughters of David and Elizabeth (Smallwood) Losh. Your ancestor is listed as Fannie Losh, who married Abraham Sandy and lived and died in Gilmer County, WV.