Did all the baptisms you have listed take place in the IoM?

Where did Robert Kennish (bapt 1833) and Agnes Postlethwaite get married?

Where did John Kinnish (bap.1805/6) and Jane Greenwood get married?

The IGI has an extracted entry for JOHN KINNISH bapt 24 NOV 1805 Lonan, Father: JNO KINNISH, Mother: CATH KNEAL. They married 3 JAN 1805 Lonan.

The IGI also has a bapt for JOHN KINNISH on 21 FEB 1779 Lonan, son of NICHOLAS KINNISH, who could be this John.

In the 1841 census (rounded adult ages; no relationships) for Lonan, one of the families at "Baldorin" was John Kinnish 65, Catharine 60, Thomas 31, and Ann 20.
[Thomas bapt 03 APR 1809 Lonan son of John Kinnish & Cath Kneal. Ann bapt 13 SEP 1818 Lonan.]

The only John Kinnish b.c.1805 I could find in the IoM in 1851 was b.Maughold with wife Ann (living in Onchan).

Sue