Think this is his baptism:
Jno. Richardson Duncum bp.1802 (full date not given) Holy Trinity Hull, son of David and Keturah.
possibly a sister:
Susannah Dunkin b.30/11/1806, bp.2/12/1806 Fish Street Ind. Kingston upon Hull, dau. of David and Keturah.
David Duncum married Keturah Richardson 6/10/1801 Hull.
The above all on familysearch.
FindMyPast shows: David Duncan bc.1772 bur.8/9/1827 Wesleyan Methodist, Kingston upon Hull.
FreeReg: Keturah Duncan bc.1781 bur.28/7/1807 Kirk Ella - Abode Hull.
Looks like David remarried (no status given on online record):
David Duncan married Margaret Umpleby 23/10/1808 Sculcoates and they had the following children, all baptised Wesleyan Methodist, Kingston upon Hull:
Samuel b.3/2/1811, bp.1/7/1818
Richard b.3/1/1814, bp. ditto
Margaret b.5/10/1815, bp.18/10/1816 - bur.3/9/1819
David bc.1816-7 bur.12/4/1817 (shown as son of David and Margaret)
David b.7/3/1818, bp.1/7/1818 - bur.30/5/1821
Jonathan b.17/11/1820, bp.19/7/1821
David Fletcher b.17/1/1826, bp.27/5/1826
In 1841 Samuel and Jonathan are living together in Kingston upon Hull
Margaret Duncan (2nd wife) bc.1784, bur.15/6/1831 Wesleyan Methodist, Kingston upon Hull.
Annette