There are a few developments I thought I'd share with you. Caswell & Mazarine Carper had younger brother named Elkanah. He was born in 1819 or 20. He is the 3rd male child on the 1830 census under Joseph Carper. He can be found in the 1850 in Baltimore, MD, in the household of his father-in-law Jonathan Wilson, and listed as a medical student. He is listed as a 1851 grad of the Maryland School of medicine in a list of alumni. He died in 1852 or 3. Property tax records & deeds that I went through at the Craig Co courthouse support his relationship with Joseph - they mention "filial affection".
I have located and my sister photographed graves of Mazarine, Eliza, their daughter Mary (Marie) Evelina Heinekamp & her child.
A Mr McPherson from Find-a Grave sent me a copy of Mazarine's death certificate. His mother's maiden name may not have been Foster as listed but Summerfield. I haven't found out which Summerfield is her father but Joseph Carper acquired a lot of land from Richard, William, and John Summerfield who were neighbors. There's little or no connection to a Foster family, but a strong connection to the Summerfields. I haven't changed her name in my tree yet. I want to go back to VA and check out the books again.