I am researching the Boston Investigator and came across your post.I subscribe to the New England Historic Genealogical Society and thus have access to all vital records of Massachusetts.I quickly looked up these for you.I hope this helps!
Josiah P. Mendum, Male, Widowed, aged 79/6/4, Cancer, died in Melrose, Publisher, born in Kennebunk, Maine to Nathaniel Mendum and Lydia Goodwin, who were from Kittery, Maine and Wells, Maine respectively. (Melrose Death Register, Vol. 419, 1891, p. 289)
Elizabeth Mendum, Female, Married, aged 48/10, Consumption [tuberculosis], died in Melrose, born in England to Jesse & Harriett Munn, both born in England. (Melrose Death Register, Vol. 248, 1872, p. 225)