Finally found the reason several generations of people are named like this: "[First Name] Rittenhouse MARKLE". It was because Jacob MARKLE was indentured at the Rittenhouse papermills in 1765 [age 11], married the widow of a Rittenhouse (Catherine nee SCHWARTZ) late 1700s, managed the ailing mills in Jacob R's old age, then Rittenhouse died no issue 1811. So Jacob and Catherine had children of both Rittenhouse and MARKLE surnames.

BTW, there are others named "[First name] MARKLE Rittenhouse", just to confuse things.