Thanks so much, amondg! I think those are her parents, and I'd found some of those baptisms but (crucially) not Edward's, which fits the 1841 record perfectly.
I'd found two others likely to be theirs:
* William, bapt 21 Jan 1810 in Holborn, parents James Holloway and Mary
* William Henry, b 1821, bapt 19 Aug 1821, d 26 Aug 1824, Southwark; James Holloway & Mary Ann (living at Great Suffolk Street)
Thanks again!
Andy