Just a couple of things.... James gravestone says...on PANB site
SHERMAN, James H Born 1844 Died 1908 Cemetery Rockland, York County
BUT in a marriage record on familysearch.org of one of their daughters in Calais, Maine in 1902 it says James and Sarah are dead. Maybe someone put the wrong date on the gravestone? Maybe somebody fibbed about the parents being dead ( elopement?)
I looked for James/Jane in the 1851 NB census automatedgenealogy.com and couldn't find either.
No wonder you having problems with this family! By the way, I have run into several instances of childrn listed by wrong sex and name.