I think that Moore sent this letter to John Durancé George, and that ‘your uncle’ referred to Samuel Cartwright.
Durancé’s sister might have been Annette, who died at Romsey on 1st January 1848; or possibly Catherine, wife of Nathaniel Jackson,
who died early in 1846 in Islington.
Moore has written out the first two verses of the four-verse poem The Minstrel Boy to the war is gone which was first published
with a musical setting by Sir John Stevenson in the fifth part of Moore’s A Selection of Irish Melodies in 1813.
His address of 'Sloperton' is Sloperton Cottage at Bromham, Wiltshire.
Moore is considered Ireland's National Bard, and is to that country what Robert Burns is to Scotland. He died in February 1852.
Further reading: Wikipedia article