Going on the birt info you already had a checked the births for Mary Ann McKEACHIE again.
This time found a possile born 19 OCT 1855 Wigtown, Wigtown, Scotland
Parents Jonh McKEACHIE & Margaret THORBURN
This was from the LDS site which has pretty good coevrage for Wigtown.
I didn't find a marriage for this couple though and when checking 1851 census for margaret THORBURN there were no matches although a few for John McKEACHIE.
The 1871 census info you have, was this form Scotlands People. If so you should be able to view the entries on there by paying a £6.00 fee which gives you 30 credits.
Mine have now exoired so i can't view them at the moment.
I also checked again for Hugh's birth trying the spelling variation and came up with the following
Hugh McGIBBONY christened 04 OCT 1849 Glasserton, Wigtown, Scotland
Parents Hugh McGIBBONY and Elizabeth DAVIDSON
This was the only possible in the whole of Scotland for any year!
Rememer the census can be mis transcribed or information noted incorrectly so it is worth considering these possibilities.
I didn't find a marriage for this couple either.
I did find 2 more children for them.
HUGH MCGIBBONY - International Genealogical Index
Gender: Male Christening: 04 OCT 1849 Glasserton, Wigtown, Scotland
2. JAMES MCGIBBONY - International Genealogical Index
Gender: Male Christening: 20 JUL 1852 Glasserton, Wigtown, Scotland
3. JANE MCGIBBONY - International Genealogical Index
Gender: Female Christening: 10 OCT 1854 Glasserton, Wigtown, Scotland
Another thing to try is going to the following site:
http://freepages.history.rootsweb.com/~leighann/index.htmlThis site is a great help to anyone researching in Wigtown.
If you look down the left column you will find a surname link. Click on that and go to the M.
The si someone who is researching the McGIBNEY surname and all it's spelling variations. If you click on the number beside the entry this will give you her details to contact her.
The same applies for your McKEATCHIE surname too,
Good Luck and i hope this helps you along!
Amanda