Bulmer's father was born in Armagh, although he later lived in Monasterevin, County Kildare, and was said to be a Gladstonian Home Ruler in politics, while his mother was an English-born radical. In 1911 she was reported to be on a suffragist procession in London and was long involved in Belfast cultural activities. She gave a lecture, entitled "Some Ulster Souterrains" as the Belfast Naturalists' Field Club's representative in 1901 at the British Association's annual meeting in Leicester. With the poet Alice Milligan, she organised the Irishwomen's Association, whose home reading circle met in the Hobsons' house. Hobson began at 13 to subscribe to a nationalist journal, "Shan Van Vocht", published by Milligan. Soon after he joined the Gaelic League and the Gaelic Athletic Association.