Hi Robert, I'm afraid I can't add anything further concerning your ggg-g'father, Admiral Sir Richard Devonshire - all of the information I have concerns the marriage of Richard Devonshire and Loveday Warren in Truro, Cornwall on 29 May 1828 and their 3 children - all of which you appear to have.
John Ferris Devonshire was born about 1774 and in 1801 as Commander JF Devonshire he was in command of the 30 gun sloop HMS Dart in Nelson's fleet at the battle of Copenhagen - see
Following the end of the Napoleonic wars, John Ferris Devonshire became a Magistrate in the Cornwall Quarter Sessions Court in Truro.
My information is that John Ferris Devonshire and his spouse Harriet (possibly Harriet Kempe) had the following childern - Elizabeth Warrick Devonshire - baptised 20 DEC 1803. John Kempe Devonshire - baptised 1 JAN 1805 Charles Henry Devonshire - baptised 21 MAR 1806 Amelia Devonshire - baptised 4 OCT 1808 James Kempe Devonshire - baptised 22 MAY 1818 All baptisms took place in Truro, Cornwall.
I suspect that John Ferris Devonshire was the son ofThomas Devonshire and Elizabeth (Ferris?) who had the following children - Betsy Ferris Devonshire - baptised 23 JAN 1770 Thomas Devonshire - baptised 9 JAN 1772 John Ferris Devonshire - baptised 27 MAY 1774 Henry Devonshire - baptised 11 DEC 1775 James Devonshire - baptised 4 AUG 1779 Mary Devonshire - baptised 4 JAN 1785 All baptisms took place in Truro, Cornwal
You will find a reference to Thomas Devonshire in the A2A web site together with a ? Ferris, who is most likely the father or brother of his wife ( I can't remember his christian name).
All of the above needs verification as to its authenticity - the IGI does contain a significant number of errors.
My own Devonshire ancestors are from Maker in Cornwall, just across the river from Plymouth Dock, now known as Devonport. My ggg g'mother, Thamzin Devonshire married Lt. George Thomas Wingate, RN in 1801. He was captured by the French at Callais in 1805 when the gun-brig that he commanded, HMS Biter was wrecked. He spent the next 8 years as a POW in Verdun where my gg g'mother was born.
Regards, Mike Hallinan Deniliquin, NSW, Australia.