Nettie - I have the will of George Arthur, farmer at Longside and formerly shipmaster of Peterhead. He died in 1867 and in his will he leaves his estate to his nephews Andrew and Robert Shewan, shipmasters of London.
I believe that Gordon Arthur had (at least) two sisters - Jane who died in infancy and is buried with her parents in Peterhead and Margaret - and (at least) three brothers, Andrew, Thomas and George. Andrew was a surgeon/druggist. Thomas was a seaman.
The three brothers all had daughters. I've found baptisms for two daughters of Andrew, and a daughter of George, but at the time Andrew and George weren't married. I don't know what became of these daughters. Thomas had a daughter called Isabella who lived to a ripe old age. I haven't confirmed who Isabella Arthur's mother was, but I do know the maternal grandmother was Isabella Rae who had children by two marriages - the first husband was a Riach and the second was a McKinnon.
I think Gordon Arthur's maternal grandparents were Thomas Lendrum and Jean/Jane Cassie of Cruden and that Mary Lendrum who married George Barclay was the maternal aunt of Gordon, Margaret, Andrew, George and Thomas. I think that another aunt was Elizabeth Lendrum who married John Lillie. This is about one of their descendants:
http://rbg-web2.rbge.org.uk/bbs/Learning/Bryohistory/Bygone%20Bryologists/DAVID%20LILLIE.rtf