The 70 year old John Shimmin looks like John's father. Note Ann 50 with "Farmer's wife" crossed out corresponds to her being 61 and 71 in 1851 and 1861.
One possibility is that there was some confusion at the time and only one John was recorded.
Also in 1841 John's and Ann's daughter, Elizabeth, was in Malew with her sister and brother-in-law, Ann & William Cowley.
There are two potential ( untranscribed) wills in 1865 & 66.