Copeland family trees give the death date of Moses Copeland as Oct 19, 1852.
No cemetery records found for any Copelands found in Mobile much before 1900.
The service record doesn't mention any family relationship.
The company mentioned came from Mobile, Moses Copeland spent most of his life in Mobile, and he appears in the household of the elder Moses Copeland in Mobile in 1850. I've assumed Moses to be the son of Moses and Elizabeth Copeland of Mobile.

In 1830 Moses Copeland was reported in Covington County MS. On Dec 19, 1835, he married Elizabeth Edwards in Washington County AL. On the census of 1840 and his family are living in Mobile. Without a fair amount of time and effort to identify all his children, I would not guess at the relationship of either Moses Copeland to anyone else. However, since the 1850 census shows three girls plus Moses in the household of Moses and Elizabeth Copeland, and the 1830 census lists several children, we can assume that Moses had older half brothers and sisters from his father's first marriage (ca 1810).