I found some information on the relationship between Nemiah, Ira, and Chester in an 1879 History of Cuyahoga County. The information was given as part of the history of Newburg Township, under the heading "Early Settlement". A paragraph in the history states:
"When Mr. Marks settled in Newburg there were on the Bedford road in Newburg the Jewetts, John and Samuel Brooks, and Nehemiah Wallace, with his three sons, Ira, Chester, and Jefferson, the former two being married. Chester is still living in Morrow County, in this state".
So it appears that Ira and Chester were sons of Nehemiah. The fact that they were married, would be why they were enumerated seperately on the census while Jefferson was not. No mention of Ethan Allen Wallace. Hope this helps some -- Richard