Since it is not my Knowlton line, I have not done any original work on these people except for the census (no land records, wills, etc.). However, I would say this is the correct John because of proximity of Jeremiah and, as you say, their sister Eunice Upton. The errors are slight, the sort that happen when the wife is older than the husband, very common in Knowlton families. The little girls may have been forgotten (not in history) or died. There are three boys young enough to be the sons. The young man could be someone's brother. John's death must be 1831 or 1832, not the third choice I put in an earlier message.
John had older brothers Ebenezer (961), Jesse (962), and Silas (963) also. Their father John (409) "served in Capt Joseph Leland's co., Col Abner Perry's Regt, Rhode Island Alarm, July 1780, and for three years previous." Stocking, p 79. He came from Sherbourne, MA, and died in Dublin, NH, April 1835.
Hope I have answered all your questions and wish we could get Terry McGinnis to respond since she is the one descended from John and Lois. Have you tried to reach her?