Hi Peter
"A week is a long time in politics" Harold Wilson 1964
" A hundred years is no time at all in genealogy" Me. Just now
Kempston PRs have been extracted onto the IGI (
www.familysearch.org - which is playing up something chronic at the moment) so if they're not there the chances are that they were from another parish or weren't baptised for whatever reason, usually non-conformity. I see they were married in Kempston in 1808. Have you checked the parish register to see if a parish of residence other than Kempston was quoted for either/both of them? If not try a new look up request, as these records have been transcribed and are much more accessible.
On the IGI there's a baptism of Avice Inskip in Bromham on 12 April 1789, daughter of John and Mary. Bromham adjoins Kempston. There's a burial of Avice Mobbs age 57 in Kempston on 19 March 1846. So the age fits perfectly.
There's a burial of John Mobbs age 53 in Kempston on 7 May 1838. The IGI has a baptism of John Mobbs at Kempston on 3 Jan 1786, birth 8 Dec 1785, son of John and Jane Mobbs
If you're a believer in naming patterns two of their daughters were named Jane and Mary and they had a son John (but every family had a son named John!)
Regards
David