I am planning to research the Kirby family in the future but do have some info now. My triple great grandmother was Anne Kirby (1785-1858), called Nancy, She was the daughter of Francis Xavier Kirby(c.1763-1831) and Elizabeth Collard (1764-c1802). Her uncle was John Baptist Kirby. Francis, Elizabeth,and John Baptist are all buried at St. John's Church, Broad Creek.
My limited research shows Anne's father, Francis Xavier Kirby, was the son of Richard and Mary Kirby. This Richard was born "before 1730 in Prince George's County, MD" and died 22 Oct. 1785 in PG County, MD. One of his children was Sarah who married Theodorus Neale. This info came from rootsweb from "1658-1758 Charles County MD Families "The first 100 years". It gives a lot of info about the line.
Sarah would have been my ancestor Nancy's aunt. And your Sarah and my Francis Xavier were brother and sister.