I have just read some of your blogs about the Graves family of Admirals from Ireland and Devon. They are my grandmother's family and I know some information which could be of interest to you, Rear Admiral David Graves (1746-1822) was not the son of Admiral Thomas, (1680-1755) but of Thomas Graves and Mary Neave.
He had an elder brother Samuel b.1741, who married Mary Semple and had two sons Captain William Graves R.M., who died 21st September 1853 and Alexander b. 1784 who served as a midshipman aboard HMS Pickle which was commanded by Captain John Richards Lapentiere who had married 2ndly Mary Graves a daughter of Lt. John Graves of Gravesend by his wife Elizabeth nee Dowling a daughter of the Rev. William Dowling.
Jane Hervey, could have been the governess to David, George and Mary (see above) and they may not have been siblings, but cousins. William Graves (1724-1801), the elder son of Admiral Thomas Graves (1680-1755) was a lawyer and a help to all the family in trouble.
David Graves is referred as a nephew by Admiral Graves, (1713-1787) together with brothers Samuel, Thomas (later Admiral Sir Thomas 1747-1814)), John and Richard, in his will.
There will be a book soon to be published about Rear Admiral Richard's wife and family.
I thank you for contacting me! I do happen to have more than a passing interest in the Graves family, which 'happened' to me by coincidence a few years ago, focussing particularly on Samuel Graves and his wife, Margaret Spinckes.
Naturally, I also have an interest in the family around them, which is why I am grateful for your comments. I fear however that there may be some confusion here as to the identities of David Graves and his siblings.
I have reviewed the wills of both Thomas (1680-1755) and Samuel (1713-1787) Graves in order to find any possible information on David, George and Mary Graves. Neither are mentioned in Samuel's will, but Thomas' yields the information that [...] aforesaid being the children born of the body of the said Jane Hervey.
Will of Rear-Admiral Thomas Graves. National Archives reference number PROB 11/821/71
Jane being explicitly named as the mother of all three, not as you suggested perhaps serving in the capacity of governess or other third-party caregiver, implies that David, George and Mary were at least half- if not, wich would seem more likely to me, full siblings.
David, George and Mary are without a question the product of an intimate relationship between Jane Hervey and a male Graves of the Thanckes household, meaning either Thomas, or his sons William and Thomas may have been the father.
Given that the children are mentioned in Thomas Graves' will, but without any specification as to their relation to him (compare e.g. to "my said son William Graves" or "my eldest son Thomas Graves") heavily implies that they were his own, illegitimate children.
The Samuel Graves born in 1741 is a somewhat greater mystery to me, as the only Samuel in that generation I am aware of is Rear-Adm. Samuel Graves (1741-1802) who Catherine Featherstonehaugh and lost an arm during his service in the American Revolutionary War. This Samuel was the son of Rev. John Graves, and the nephew of Admiral Samuel Graves (1713-1787). I wonder where 'your' Samuel Graves, born in the same year, figures into the family tree.
Returning to David, I really could not find any bequest to him in Samuel Graves' (1713-1787) will (National Archives reference number PROB 11/1151/194). He bequeathes some money to his cousins William, Thomas and Anne Graves, Thomas Graves' (legitimate) children from his marriage to Elizabeth Budgell. Other family members who are mentioned in his will are his wife Margaret, nephews Samuel, John, Thomas and Richard, the sons of his brother Rev. John Graves, his godsons and grand-niece.
David later had several illegitimate children of his own; his will (National Archives reference number PROB 11/1664/357) is the only source I have on his siblings and children.
The way I see it, and to illustrate my research, this is what the family tree would look like. Please note that it is of course simplified, leaving out a great many people as it is geared towards showing the relationships discussed above.
I am excited to learn that there will be a book on the in-laws of Richard Graves. From all I have read, his wife was quite a character who at one point proclaimed that she was afraid of the trees surrounding Hembury Fort House, which is why she needed him to move to the city with her.
Do you happen to know more about the book project on the Colleton family?