Severance claims both daughters survived their parents but daughter Lena's grave marker verifies she predeceased them. (Severance, B. Frank. Genealogy and biography of the descendants of Walter Stewart of Scotland and of John Stewart who came to America in 1718 and settled in Londonderry, N.H. Greenfield, Mass. : T. Morey & Son, 1905, pg. 125).
I sumise the following about this family. Franklin married Jennie first and had a daughter, Lena P., with Jennie. This is indicated by Lena's grave marker found on findagrave.com. Severane notes only his second wife, Sarah Stewart, and that two unnamed daughters who survived Franklin and Sarah. Lena was born 8/22/1866 and died 11/3/1878, hence Jennie died or she and Franklin divorced after 8/22/1866, and Franklin married Sarah and their two unnamed daughters were born after 8/22/1866.
Company C, 115 NYS Volunteers (findagrave.com)