castellian/castellano

i am trying without sucess to find any information on my gggrandfathers family eg his parents brothers and sisters ect.
my gggrandfathers name was matthew castellian or so i have been led to belive but when posting on italian ancestor sites i have since been told there is no such name in italy and that the name is probably castellano.
my gggrandfather was born in naples italy 1842, before he came to live in liverpool uk, where he married and had several children, i am assuming he came here about 1862 maybe earlier but he does not appear on any british census untill 1871, he married in nov 1863, i sent for his marriage cert but on it it gives his name as costello!!!!!!! on the census throughout the years untill he died in 1901 his surname was spelt different on each one!!!! i would love to find out about any family he had back in italy
trish