Amanda's birth was registered Chepstow, so birth places for these 2 wrong way around possibly?
Amanda Mary Shellam sept qtr 1853 Chepstow vol 11a pg 9
The bad news is that Mary Ann's maiden name was Jones from marriage ref I gave you above. Also, I'm not finding the family in 1871. I thought I'd found a re-marriage for Mary Ann in Chepstow, and although she's in Cardiff for the 1871, she's younger and no sign of any Shellams in the house.
But I have found some more generations
1841 Brookend, Wollastone, Glos H0107/369/6 folio 14 pg 3
George Shillam 40 shoemaker
Jane 40
Alfred 14
George 5
Amanda 10
Jane 3
Martha 90
all except Martha born in county.
I was searching for anyone called Shellam anywhere in 1871 and spotted George in Woolaston - cordwainer and postmaster, and was pleased when this census makes it look like the right man.
As for the Giles family, I'm beginning to think that Ann might have exaggerated her father's occupation. There is this family in 1861
Cardiff St Mary RG9/4034 folio 72 pg 14
Thomas Giles head mar 34 coal dealer b. Llantrisant
Margaret wife 33 b. Pendoylan
David son 6 b. Cardiff
Hannah dau 3 b. Cardiff Margaret dau 2 b. Cardiff
Thomas son 1 b. Cardiff
Abbey Hanton servant 23
can't read the address possbily east something. The family don't seem ever so keen on registering the births of their children either. I did spot the marriage
Thomas Giles dec qtr 1852 Cardiff vol 11a pg 315 on same page Margaret Davies - oh no, double whammy
I've found this family in 1871, but no Hannah/Annie with them - no death registered either so still possible. Thomas is now a labourer. RG10/5362 folio 114 pg 33 at 33 Frederick Street A*c*t*y has them as Gales, but it's Giles on the census itself. haven't spotted them in 1881 either.