only Arthus in 1881 census (it is online) is in Parish of Patrick - address Kiondhoag (Kione dooag, 'end of the black land,' i.e. marshy. - sometimes Kiondhooag,Foxdale)
SHIMMIN Robert Head M 48 Farmer 20 Acres born Patrick
SHIMMIN Margaret Wife M 36 --- Marown
SHIMMIN John Son U 19 Lead Miner Malew
SHIMMIN Daniel Son U 15 Lead Ore Washer Malew
SHIMMIN Edward Son - 10 Scholar Malew
SHIMMIN Arthur Son - 7 Scholar Malew
SHIMMIN Richard Son - 3 --- Patrick
SHIMMIN Sarah Daur - 10months --- Patrick
SHIMMIN Catherine Daur U 18 General Serv (Dom) Malew

thus, assuming correct identification, looks as though they moved to Patrick c.1878 (no Shimmin in Wood's Atlas of 1863)