I have recently found the birth records of William Grant and his siblings as follows:
Church: St Mary Magdalene, Taunton, Somerset
Charles Gordon Grant, born 25 Feb 1788, baptised 24 Apr 1788 and 14 Jan 1801
William John Grant, born 14 May 1789, baptised 24 Nov 1792 and 14 Jan 1801
Maria Vincentia Grant, born 3 Nov 1792, baptised 23 Nov 1792 and 14 Jan 1801
Ellen Gordon Grant, born 20 Dec 1795, baptised 14 Jan 1801
In each case the parents are given as John and Ann.
The following may be the marriage of the parents:
Church: Shadwell, St Pauls (location: London, East End)
John Grant and Ann Cottell, 13th July 1784
St Pauls at Shadwell had connections to the Royal Navy, I guess due to its location on the Thames.
Below is the full description of the family connections from William Grant's Naval biography:
Quote
William Grant was born 14 May 1789, at Taunton, in Somersetshire, and died 1 Dec 1845. He was son of Capt. John Grant, who obtained a medal for his services in the 40th Regt. during the first American war, and who afterwards, when belonging to the Prince of Wales' or Leicestershire Fencibles, fought in Ireland during the rebellion of 1798. One of his cousins, Wm Cottell, Lieutenant R.M., was mortally wounded on board the ROBUST 74, at the defeat, in the latter year, of a squadron under Commodore Bompart; and another, the late Capt. Jas. Cottell, R.M., who died in 1842, served in the TONNAT at Trafalgar. He has left a brother, a Surgeon in H.M. 10th Regt., now at Calcutta.
This officier entered the Navy, 13 Sept, 1805...
He went on half-pay in Sept. 1815. having been promoted to the rank of Lieutenant on 11 of the preceding Feb., and did not again go afloat.
Lieutenant Grant married in 1837.
Unquote
CM
Sydney, Australia