I don't have a whole lot of facts in regards to John and Barbara Daubenmeir but I can tell you that the various church books and censuses I do have for Hocking County mispell the surname so badly that it's no surprise that you're having difficulty.
However, I did find John and Barbara living alone on the 1880 census for Marion Township, Hocking County, OH listed as John A. and Barbara DAUBENNIER:
John A. Daubennier, 77 years old, birthplace; Baden, Occupation; retired farmer, father's birthplace; Baden, mother's birthplace; Baden.
Barbara Daubennier, 72 years old, birthplace; Baden, keeping house, Father's birthplace; Baden, mother's birthplace; Baden.
Also, I found them buried beside each other listed in the St. Emanuel Lutheran Cemetery, Marion Township, Hocking COunty, OH:
DAUBENMIER, JOHN ADAM--died 6/15/1887; age 84 years, 4 months, 6 days.
DAUBENMIER, BARBARA--HIS WIFE--11/15/1808-5/25/1898
The next tombstone beside Barbara is:
The way I even found it was from my local Family History Center, I got on Ancestry.com and did a search of the 1880 census from someone that I KNEW would be in the Marion Township, Hocking County, OH. Once I got onto a page of a census record for there, I just searched backwards and forwards of previous households, looking for Daubenmiers spelled any which way. You could do the same thing and look for Fossler families. I notice that there are also Fassler families on the censuses for that area.
Here is the rest that I have on this family (it was sent to me from a friend researching the Shull families):
9.BARBARA SHULL (MATHIAS2, JACOB FREDERICK1) was born October 22, 1835, and died August 9, 1888.She married FRANK DAUBENMIER June 10, 1855.He was born January 2, 18331, and died August 8, 1918.
Children of BARBARA SHULL and FRANK DAUBENMIER are:
i. ANNA MARIE DAUBENMIER, b. April 2, 1856; d. June 18, 1949.
ii. EMMANUEL DAUBENMIER, b. October 11, 1857; d. April 29, 1949.
iii. CHRISTINE BARBARA DAUBENMIER, b. January 8, 1859; d. February 27, 1940.
iv. JOHN ADAM DAUBENMIER, b. June 6, 1861; d. August 12, 1861.
v. LAURA ELLEN DAUBENMIER, b. December 31, 1877.
Hopes this helps.Good luck in your research.