It seems unlikely that two twins could be born more than a month apart - I would suspect the date is wrong for one of the two persons. If we assume Theodore's birth date is accurate then I would consider the following possibilities:
1. If the date was derived from an age calculation I would guess 1816 or 1818. While it does happen, It is less common to see a calculated birth that specifies a month, so I would guess this is not the case.
2. Not having the benefit of the source documents the dates are derived from I would consider that an author's penmenship can somtimes cause confusion. 1's and 7's are perhaps the most frequently confused, but I have also seen cases where 2's are readable as 1's or 3's, as well as 3's that look like 8's, interchangeable 5's and 6's, and 4's and 9's.
With this in mind I would try and find records from 1811, 1821, or possibly 1827, as any of these would fit with the existing dates of the children's births
3. It is possible someone entering the record merely made a typo... given the pattern of this family where there is a child born approximately every 1-2 years, I see gaps at 1811, 1815, and possibly 1821 - of course there is usually little record of stillbirths at this time, and there are 2 children with no date of birth.