Twin Errors

Six sets of twins ( a boy and a girl in every case) made several errors in their history and geography examinations; and it was noted that every girl made precisely the same number of errors as her brother in the two subjects. Name each pair of siblings and their surname and work out how many mistakes each made in their history and geography examination papers.

1. The boy ( not Luke ) whose sister is Louella made more history errors than Sammy.
2. George did better in history than the boy surnamed O'Connell, who made either one more or one less geography error than the twins surnamed Dean.
3. Anne made either one more or one less geography error than Louella.
4. The twins who made 11 geography errors didn't make exactly 11 history errors.
5. David and his sister made either one more or one less mistake in the history exam than the twins who made 14 geography errors.
6 Edward and his sister did worse at history than the pair who made 15 geography errors. Edward made one more error in the geography exam than Luke.
7. The McCall twins didn't make one less history mistake than the Vole twins
8. Susan ( who made seven history errors ) made one less geography error than the girl who made one less history error than Anne.
9. The twins surnamed Waters made one more history mistake than the twins surnamed Seal, who made more geography errors than the McCall twins.
10. Gail made one more geography error than the girl who made one more history error than Louella.
11. Martin made either one more or one less geography error than his best friend and his sister, who made more history mistakes than Diane.
12. Wendy and her brother ( who didn't make a total of eight history mistakes ) didn't make as many errors in geography as George and his sister.

Brothers are - David, Edward, George, Luke, Martin & Sammy.
Sisters are - Anne, Diane, Gail, Louella, Susan & Wendy.
Surnames are- Dean, McCall, O'Connell, Seal, Vole & Waters.
Geography errors are - 10, 11, 12, 14, 15 & 16.
History errors are 6, 7, 8, 10, 11 & 12.