Brian, you wrote:
Robert Looney (bc 1795 Maughold) married Betty Sayle 17 May 1821, Maughold.

Maughold (original) reg has:
Robert Looney and Elizabeth Sayle married 12 May 1821.

Robert son of Robert Looney & Margaret Cannell 20 Oct 1794. Private baptism.

Robert LOONEY 75 Near Port y Vullin buried May 27 1867

Elizabeth LOONEY 85 yrs. Port-e-Vullen Maughold buried 1 Aug 1884.

These were their children bapt in Maughold:
Mary dau of R Looney/ Elizabeth Sayle Parish Church 6 Jun 1819 Illegitimate.
Robert son of Robert Looney/ Elizabeth Sayle Parish Church 13 Apr 1821. Illegitimate
John son of Robert Looney/ Elizabeth Sayle Parish Church 1 Jan 1824
Mary Ann dau of Robert Looney/ Elizabeth Sayle Parish Church 5 Mar 1826
Thomas son of Robert Looney/ Elizabeth Sayle Parish Church 16 Oct 1836

No sign of them on the other dates you had, or of Betty 25 Mar 1828 Maughold.
Only Elizabeth dau of Robert Looney/Jane Sayle 23 Mar 1828, so wrong mother?

Sue