He is almost certainly the brother of Peter Allen, M.D., born 1 July 1787 in Norwich, CT.Dr. Allen and his wife, the former Charity Dudley, moved to Kinsman, Trumbull, Ohio sometime before 1814.
I have the following siblings for Peter Allen: Benjamin, born 25 May 1784 Daniel, Francis, Lois, Betsy, Lucretia
I have as their parents: John Allen, born ca 1762, Norwich, CT Tirzah/Tirza Morgan, born ca 1754, Norwich, CT Married in Groton, CT 27 April 1783
John Allen may be the son of Benjamin Allen and Rebecca/Rebeckah (Arnold?) who died in Norwich, possibly 1783.
Tirzah Morgan was the daughter of Peter Morgan, b 1705 and Elizabeth (Whitmore?) b 1716.
I don't have unimpeachable sources for most of this, although I'm fairly certain of the name of Peter and Benjamin Morgan's parents, especially the mother (Tirza Morgan).The fact that they named their eldest after the paternal grandparents lends additional credence.