He married Sara Mundheim, a nurse in a Washington military hospital. She later died, and Karpeles married her sister.

http://www.tshaonline.org/handbook/online/articles/fkajk

When Sara died during the birth their third child, Sara's sister came to care for the children and, later, married Karpeles. Together, they had three children.

http://www.jewishvirtuallibrary.org/jsource/biography/karpeles1.html