Elizabeth (Stephens) Bryce (1826-1880)

She is generally referred to as the sister of the explorer John Lloyd Stephens, but according to ancestry.com his father, Benjamin, died age 32 in 1816 apparently tens years before she was born. Ancestry may be wrong as elsewhere Benjamin (a native of New Jersey who became a successful merchant in New York) is noted as having been one of the longest-living merchants in New York. The last query is that Elizabeth was apparently 21-years older than her supposed brother, John, and so perhaps she was the daughter of John's elder brother, Benjamin Jr., who was born in 1804? If you can help solve the riddle, please email.