Thanks so much!
some of these gaps and bits of extra info are really helpful - especially the glaringly obvious (now!) bit about Old Congreve being a Farmer on the marriage certificate so more likely the father.
RE: Camilla Bennett b. 1844 Stowe - I saw she was recorded as Bennett but let myself believe it was just messy handwriting! The extra connections round there are helpful.
@Mckha489 I also considered whether the ages had been changed, but it would have required her to stay 14 from one census to the next! I keep thinking if I could find that missing census record for Helen Elizabeth from 1861 that would unlock it.
Also, if I've understood correctly that Mary Hadland (who married William Hadland in 1839) was born Mary Banwell, then that explains the Neice connection to Helen Elizabeth. I can't remember if I found proof that Mary Ann Banwell was born Hadland or had just made an assumption, but that might unlock different possibilities...