Susan,I found various records which relate to your family.
1855 Massachusetts census: Boston,Ward 11,Suffolk,Mass William Lowry age 45 Mary Lowry age 50 Susanna Lowry age 24 William Lowry age 20 Jaime Lowry age 18
1860 US Census; Hingham,Mass William Lowry age 60,born 1800 in Ireland Mary Lowry age 60,born 1800 in Ireland James Lowry age 23,born 1837 in Ireland
1865 Massachusetts census: Hingham,Mass William Lowry age 60,born Ireland @ 1805,ropemaker Mary Lowry age 63,born Ireland @ 1802
I could not locate a marriage for Susanna nor James but James must have married between 1860-1865.As for Susanna I cannot locate any record for her.Perhaps she died?
Marriage cert: groom:William Lowry groom's father:William Lowry bride:Ann Sweeney bride's father:Daniel Sweeney married:25 August 1855 place:Roxbury,Suffolk,Mass
I did not locate Lowrys in Boston passenger lists.Could they have come in through New York?
I did find 2 births of children to James and William which struck me a bit odd.
Susan Lowry born 4 Feb 1867 in Lyman,York,Maine parents:William Lowry/Ann Sweeney
Mary Jane Lowry born 22 June 1868 in Lyman,York,Maine parents:James Lowry/Mary Jackson
in both these births the children are listed as being born in Lyman,York,Maine and Hingham,Massachusetts.Do you know connection to Maine?
Also,according to death certs for Mary Lowry,James Lowry and William Jr,Mary's mothers maiden name is not coming up as Crowley.
William Lowry Sr died:22 Jan 1870 Hingham,Plymouth,Mass male age:70 married born Ireland @ 1800 parents born in Ireland died apoplexy
Mary Lowry died 3 May 1870 Hingham,Plymouth,Mass female age:78 widowed born Ireland @ 1792 parents:Peter Cowley/Polly ? spouse:William
James Lowry died:12 Nov 1881 Hingham,Plymouth,Mass male age:45 widowed labourer born:1836 Ireland father:William Lowry born Ireland mother:Mary Kallan/Callaghan born Ireland
William Lowry(Jr) died:6 Nov 1882 age 48 male born 1834 Ireland father:William Lowry mother:Jane Callan
Mary Lowry died:10 Dec 1871 Hingham,Plymouth,Mass age:24 born 1847 parents:William Jackson born Ireland Ellen Bowen born Ireland spouse:James Lowery died of consumption
Do you know if William Lowry was naturalized?I did come across the name a couple of times so it would be worth checking it out as naturalizations can have good info.I would also try to discover the connection to Maine.Hope this helps,Kim