Hi Margaret, James Logan was my great great grandfather. He died at 11 Millarston, Paisley on 11 July 1858 age 68, cause of death, old age and debility. You will find a copy of his death certificate on Scotlands People (Statutory registers deaths 559/1207). His wife, Jean Bolton died 11 March 1858 at the same address from bronchitis, (Statutory registers deaths 559/1 84), they are both buried at High Church, Paisley. My great grandfather was Alexander Logan, born 4 Dec 1855, hence the reason he does not appear on 1851 census. I cannot find a birth certificate for him, or any of his siblings, which makes me think they were born abroad. I do wonder about the Margaret Sommerville on your great great great grandfather's death certificate, where does she fit in?
Hope this fills a few gaps for you.
Lenna