John d 20 Aug. 1829, Age 35 yrs, implies b.c. 1794 (not 1796), and Mary's dates must be wrong if she had a son in 1817.
A possibility for John's bapt is JOHN MYLCHARANE Christening: 11 AUG 1793 Jurby, Isle Of Man, Father: WM MYLCHARANE, Mother: ELISABETH CHRISTIAN.

MARY GRIMSHAW possible Christening: 14 JUL 1793 Ballaugh, Isle Of Man, Father: THOMAS GRIMSHAW, Mother: CATH COWLEY.

These are the children of John M & Mary Grimshaw given in the IGI (as well as John, last message):
THOMAS MYLLYCHARANE Christening: 07 MAR 1824 Ballaugh, Isle Of Man
MARY ANN MYLLYCHARANE Christening: 02 MAR 1828 Ballaugh, Isle Of Man
PHILIP MYLLYCHARANE Christening: 20 AUG 1826 Ballaugh, Isle Of Man.

Sue