Hi Ddraig
Warning - yap yap yap coming up, read on!! 
My thoughts....
1) If Catherine's marriage cert does not state "deceased" for her father, it doesn't mean he wasn't - some certificates simply did not state it - either through omission or because the marrying child of the father did not know the father was dead (or condsidered him to be!). In relative terms, a statement that a father is deceased is more likely to be true. A father not stated to be deceased, but whose life or death is not found in ensuing years after the marriage is more likely to be deceased - especially if there is a death in the right place and age.
2) The death of Charles WARD in Haltwhistle Mar Qtr 1851. There is no Charles WARD or similar, birth in Haltwhistle 1841 to 1851. If the death was that of an infant, he may have been born elsewhere? Maybe it is your Charles' death afterall....it seemed like a stretch, to assume your Charles was alive on Census night yet be registered as deceased within the the March Qtr of the same year - within 1 or 2 days. But, on reflection it's probably not so hard to imagine it's him afterall - a couple of things could have occurred.....
a) the schedule may have been physically completed during the day hours, or in whole days& nights before the actual night of the official census night, ie: completed days earlier in readiness and expectation of who would be included on the schedule - but sometime just before or on the day of Census night , or the day after it (ie:from midnight on the 30th) he died. Either the census report we see is correct - he WAS alive on the night of Census (up to midnight on the 30th) or he wasn't alive on Census night, having died in the day or evening hours of the 30th, or a day or so before .. but the schedule already prepared and perhaps already taken away by the enumerator - was never corrected to 'remove his name' from the schedule.
b) the registration of such a death on 29th, 30th or 31st March was immediately afte the death, being done on or close to 29th , 30th or 31st March 1851 and so allowing it to get into the March Qtr. Or, and I don't know if it has ever happened ( I have a very faint memory of one of mine something similar but can't remember who) also possible in my mind is: a death occurred after the end of a quarter, but because the registrar is returning his Quarterly reports quite some time after the actual end of a Qtr, he may have decided for expediency, to include the death of a person who died
very soon after the Qtr end. Perhaps more likely to occur in a small district?
3) In 1861, Catherine should be abt 15 based on her age in 1851. She could be out working in Service and simply not together with a father who may be still alive. Charles' POB simply as Gloucestershire, doesn't help matters. Catherine - with a father who is either dead or alive, may be with maternal or paternal relatives and/or be down as another surname - the fact we don't find a marriage of her parents or her own birth record - helps that theory along, too. Or she could be called Kate, Katherine etc and/or the name WARD be mis-transcribed or mis-enumerated.
4) If Charles survived 1851 and was left with a 5 yr old daughter while coping with the grief of losing his wife and 2 yr old daughter: who knows what he might have done knowing he had to care for her as well as earn a crust. Not to mention he was up the other end of the country - possibly away from family. He may have taken Catherine to be with or near relatives, on his side of the family or on her mother's - possibly back in their native area (and a place of birth as "Gloucestershire" is a whole kettle of fish just in itself , what with border nuances with other counties). In 10 years between 1851 and 1861 a lot can happen. He may have died within that time. If he was alive by 1861 especially owing to his line of work on the Railway - he could be anywhere along the track - England, Scotland or Wales. He may have remarried anywhere, changed his type of work........
Gloucestershire, Berwick - Cardiff. Quite a bit of shifting about.
And musing on the daughter Mary - place of birth Bridgeston - is that Northumberland? Glasgow? I wonder,,,,
Cheers
AMBLY
