Pvt John William Sensabaugh, CSA - Are they the same?

Not the same -- John father of Elizabeth Brehm b. 1763 in Cumberland Co., PA; d. 1849 in Cumberland Co., PA; as per FamilySearch. Here's his profile there: https://www.familysearch.org/tree/person/details/KN8B-TQ2

Surely they both did not marry the same woman is the concern

They did not -- I have no idea where Mary Sensabaugh mother of Elizabeth (Sensabaugh) Brehm comes from as trees on FamilySearch and Ancestry both list her mother as Rachel Feininger.

Either way the two Johns and two Marys are not the same people.