Hi Rosemary, I am in the process of following up a whole range of Ackroyd families for my own research. I have looked through my notes but find I too have only the 1881 census for Benjiman (sic), but I wasn't really looking for a Benjamin.
Let me have any details you have for Ben, Joseph and their parents and I will add to my list. I have access to censuses from 1861 to 1901. As Ackroyds are like Smiths in Yorkshire, some clue like an address might be useful. You mention the brothers being stone-masons. Most of my Ackroyd lines so far are also masons, seems to be a family trade but could also be a link somewhere. I try to spend about half a day each week at the LDS family history centre, so if I find anything I might be able to put a bit of extra flesh on the bones when I next visit.
Hope I might be able to help a little. Regards, Roy Ackroyd.