Hi Nicola
Just been in Oswestry Library this am.
They have fiche for the Arthur St Chapel from 1800 - 1811 and a transcript for 1813-16
In "The Old Chapel(Independent), Arthur Street, Oswestry - Register of Baptisms 1813 - 1816" I found
MARGARET EVANS daughter of THOMAS & Margaret(nee HUGHES) of the town of Oswestry, Mercer Born 17 July 1813 and Baptised 19 September 1813
JOHN EVANS son of THOMAS & MARGARET(nee HUGHES) of the town of Oswestry, Draper & Grocer Born 28 April 1815 and Baptised 29 May 1815
I had a quick look for Thomas Evans in Indexes of entries in the local paper. Did not find one for 1851 but there was a death of a Thomas Evans, Upper Church Street, in 1859, Aged 61. Didn't have time to check the entry as reader was being used. If you wish me to I will when I'm there next week.