What documentation do you have to prove that they were married in 1831 in County Cavan? It would have to be a church record as civil registration did not begin in Ireland until much later. The church record should at least name the fathers. Also, if married in 1831, and not emigrating until 1840 suggests that at least one or two children were still born in Ireland before they came to the US. The 1850 census shows children, Mary & Benjamin, aged 14 and 12, both born in Ireland.
As Margaret names a child Edward and her brother is also named Edward, one can likely assume that it is also the name of her father.