Hi Morag

Using JQ's information, I've sussed out the relationship between your John Costain b 1849 and the Thomas Costain b 1837 whose 3 children are probably the ones in Priscilla's photo. They were second cousins.

Their g grandparents were William Costain(1736-1802) and Jane Harrison. Two sons of WC+JH were John b 1769 (who married Margery Cubbon ) and Thomas b 1780 (who married Eleanor Moore ).

JC and Margery's son William b 1796 married Jane Cubbon, and Thomas b 1837 was their son.

Jean