Here is Sarah Jane, possible sister of Alfred G - her birth record lists her parents as David J Killam and Rendis Dobson.More similar names.Maybe David J is the son of the John you mentioned, b in the 1820's and you were a generation off?
Also a Fred Killam is in Somerset, ME area in several censuses with wife and children.Might be his brother Fred.And John is found in the same area at age 18, single.
New Brunswick, Provincial Returns of Births and Late Registrations, Sarah Jane Killam Birth09 May 1888Calaway, Westmorland, NB father: David J Killammother: Rendis Dobson
Canada Census, 1881Salisbury, Westmorland, NB David KillamM 32y NB Renda Killam F 27y NB
Possibly Alfred’s brother Fred https://familysearch.org/search/records/index#count=20&query=%2Bgivenname%3Afrederic~%20%2Bsurname%3Akillam~%20%2Bbirth_place%3ACanada~%20%2Bbirth_year%3A1880-1889~