Found Edward in 1861~
James Street, Rugby
RG09/2212/81/18
Ann May, w, 37, Hallaton, Lancs
Edward Mostyn Thelwall, brder, 18, booking clerk, b. Wrexham
John Knunkey, brder, 23, general office clerk, b. Truro
Looks like Rebecca Sophia died before the 1861 census:
Rossett
RG09/4277/61/11
Bevis Heywood Thelwall, widower, 41, solicitor, b. Llanfair Dyffryn Clwyd
Llewellyn, 5, b. Gresford
John Bulkeley, 3, b. -do-
Emma Baker, servant, 16, house servant, b. Chester
Not sure if there's much more to find about him and his parents

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