Thanks Colin, all useful data.
Your idea that Abraham D and Mary de C signed as guardians, extra to the two witnesses, sounds good.
I've just looked through dozens of pages of Clerkenwell marriage register: fewer than one marriage in 30 has >two witnesses - as you say, it's unusual. What is odd is how very often a Wm Webb crops up as one of the two witnesses! Perhaps he hung around the church to help out couples who needed to get married urgently and had no family handy? Maybe a drink or two in it.
Given the proximity to Aldbourne, suitable age, etc I expect you're right that Abraham Dymock was Sarah's guardian.
What I'll do for now is use all you've found to write a narrative of the likely descent, pending further info. I should perhaps make an effort with Marlborough records, such as when did Waldron's bakery disappear, etc. Sarah's likely mother being 43 at birth of her first child, I'm not expecting many siblings.
Those portrait miniatures: they're watercolours on ivory or vellum. Photography didn't get going until after 1840, and until around 1850 was mainly one-off daguerreotypes, the cartes-de-visite in multiples weren't cheap until into the 1850s. These paintings would have been relatively expensive, suggesting the Bedford Wells was prosperous: celebrating engagement or wedding I suppose.
Mike
