I think there are just too many Hugh Davies's in Llansantffraid in the 1800's!!! There is also variation in ages on the census but that was normal and could be up to 5 years out, so there is a little bit of guess work here!
Hugh Davies (birth year varies from 1835 to 1839)
1841 is at Brin y Felin, aged 6 (1835) with parents Hugh 25 (1816) a Labourer and Catherine 30 (1811), brother Robert 3 (1838) plus Thomas Thomas 70 (1771) and Martha Hughes 15 (1826) who have no relationship given
1851 is at St Ucha, aged 16 (1835) Agricultural Labourer at the home of Henry Williams, General Practitioner
1861 cannot trace
1871 is at Glanllyn, aged 35 (1836) with wife Mary 36 (1835), daughters Anne 15 (1856) and Elizabeth 4 (1867) and sons Hugh 12 (1859), John (1864) and William 2 (1869)
1881 is at Glanllyn, aged 46 (1835) with wife Mary 47 (1834), daughters Elizabeth 14 (1867) a Dressmaker and Sarah 8 (1873), son William 12 (1869) and grand-daughter Catherine 2 (1879)
1901 is at Glanllyn, aged 62 (1839) with wife Mary 64 (1837) and daughter Sarah E 27 (1874) a Dressmaker
1911 is at Glanllyn, aged 77 (1834), widow with nephew Hugh aged 18.
Hugh Davies (birth year varies from 1828 to 1831)
1871 is at Mardir Farm, aged 40 (1831) with wife Catherine 36 (1835), daughters Ann & Catherine both 10 (1861), Jane 7 (1864) and son John 4 (1867)
1881 is at Mardir Farm, aged 53 (1828) a Farmer & Agricultural Labourer, with wife Catherine 47 (1834), daughters Elizabeth 8 (1873) and Ellin 6 (1875) and sons Hugh 24 (1857) an Indoor Servant, Owen 22 (1859) a Joiner and Thomas 4 (1877)
1901 is at Ffrith y Foel, aged 73 (1828) with wife Catherine 68 (1833), daughter Elizabeth 28 (1873) a Dressmaker, and grand-daughter Catherine 9 (1892)
Then you have the following which could be linked:
1841 Hugh Davies 20 (1821) agricultural labourer living in the Yard at Nany y Cowardy (?) farme of John Wynne
1851 Hugh Davies 18 (1833) farm servant at Tyddyn Ucha for William Davies
1851 Hugh Davies 28 (1823) at Trallwyn with mother Ann 58 (1793) Farmer's widow born in Eglwysbach and brothers Evan 26 (1825), William 19 (1832) and Owen 15 (1836)
1871 Hugh Davies 51 (1820) at Tyddyn Ucha, Deunant with wife Mary 41 (1830) and daughter Mary Ann 4 (1867) + 3 servants
Trallwyn (map ref SH 794740) and Mardir (SH 797743) are very close together on the unclassified road that leds from Forddlas Bridge to the top of Bodnant Hill on the western side of the A470 (between A470 and River Conway), also not far from Ffirth-y-Foel. On the old maps there is a Mardir and a Mardir Bach.
I suspect Nant y Cowardy is really Nant y Cywarch (SH 812738) on the unclassified narrow road heading east from fforddlas Bridge.
Tyddyn Ucha is near Bryn-y-Maen at map ref SH812738
I suspect St Ucha stands for Stryd Ucha which is High Street.
Useful websites for you:
old-maps.co.uk
gridreferencefinder.com
google.co.uk/maps
Hope that is of some help ... more pieces for the jigsaw puzzle, whether they fit or not is another question!
Like me, with many of my ancestors from the same area (Glan Conway and Eglwysbach) there are a lot of duplication of names and they agricultural labourer and dressmaker seems to be the most common occupation.
Good luck!
Dave