Is this them - 1871 census?
RG 10 / 5199 / 28 / 2
Beldy, Alston
John Murray, head, m, 60, lead miner, Cumberland Alston
Mary do, wife, m, 46, do wife, do do
John Murray, son, 9, scholar, Cumberland Parish of Alston
George do, son, 5, do, do do
/
Robert Murray, lodger, u, 55, Lead miner, do do
Since you say have the references for the births of sons George and John you could get a birth certificate, which would show Mary's maiden name.