Tim, I think you need to look at the Patrick parish register copy on LDS film no. 0106738 if you haven't done so already? Parish Church of Patrick (Isle of Man) has Baptisms, 1714-1849; Marriages, 1714-1837; Burials, 1714-1832.
See their marriage on 2 SEP 1809 Patrick, as well as the bapts and burials.

Regarding William [1]'s burial, it looks as though the FHS/Brian or the LDS might have made an error with either his bapt date or his burial date:
MOORE, William infant Patrick 13 Jun 1809 [BL burial index from the FHS transcription]
Baptism from IGI: WILLIAM MOORE Christening: 18 JUN 1810 Patrick.
Also
WM MOORE Christening: 13 SEP 1812 Patrick
ANN MOORE Christening: 13 SEP 1812 Patrick. Burial? MOORE, Ann infant Patrick 1 Dec 1819
THOS MOORE Christening: 24 OCT 1813 Patrick.
MARGARET MOORE Christening: 04 OCT 1818 Patrick. Burial?
ANN MOORE Christening: 11 NOV 1821 Patrick
MARGARET MOORE Christening: 20 APR 1823 Patrick
CATHARINE MOORE Christening: 09 AUG 1829 Patrick

Sue