And a warm welcome to Rootschat from me.
FamilySearch has 7 entries for Craig born in Gibraltar - but nothing helpful for John. They are:
James CRAIG born c1841: 1871 census Everton Lancashire, furniture broker, wife Dorothy and three children; also 1901 Census Liverpool Lancashire, furniture dealer, father-in-law to William GUY
Thomas Henry CRAIG born c1836: Chelsea Pensioner (Gunner)
Nathaniel CRAIG born c1850: 1851 Census Hampshire with mother Mary (soldier's wife born Waterford)
Thomas CRAIG born c1847: 1851 Census Guernsey, son of William (soldier) and Margaret.
Rebecca CRAIG born 1883: immigration, Vermont 1924
James looks to be a good match for your John's brother.
Thomas Henry might be another sibling.
Nathaniel might be another sibling.
Thomas and Rebecca are probably not relevant to your search.
So, - no sign of your John on a census on FamilySearch. The hunt goes on!
Philip