I think it 99.9% certain that Robert and Isabella were your John's parents. I'm pretty sure that parish records for St. Mary, Bury St. Edmunds are nigh on non-existent for this period as regards to being online.
I note that your tree shows 4 children to Robert and Isabella and the only baptism that shows up online is daughter Sophia in 1814 who is listed with the surname Dibble.
Have found the marriage of Robert and Isabella:
Robert Dible and Isabella Houghton married 19/1/1808 Shropham, Norfolk - you can view the original record on familysearch - both single and of that parish. Unusually for the time, they both signed the record.
Decided to look at the parish records for Shropham in case John may have been baptised there before they made the move to Suffolk - not there. However, I did find the baptism of twins born shortly after they married:
Sophia, dau. of Robt. & Isabella Dible (late Houghton) b.28/3/1808, bp.30/3/1808.
Mary Ann, ditto
Sophia Dible, aged 1 week, buried 8/4/1808 Shropham
Mary Ann Dible, aged 5 weeks, buried 5/5/1808 Shropham
So, it looks like Robert and Isabella were from Norfolk. Whether they were from Shropham or just living there at the time is, of course, unknown. As far as I can tell, most early records for Shropham have not been transcribed online but you can view the original records on familysearch.org. A small parish so not many pages to look through.
Annette