This one for sure looks like he has an underbite. Obviously can't know for sure from pictures. But his bottom lip looks in front of the upper.
http://www.flickr.com/photos/30962728@N06/4998582435/
The other pup that you had a single picture of on the same page might too but not as bad but you can't tell by pictures.He could be fine.
With a underbite-The lower jaw is longer than the upper jaw. Think like a boxer ,bulldog or shih ztu.
With a overbite- the lower jaw is sorter than the upper jaw. Think parrot.
If you want to learn more about sheltie bites.
http://www.kennelcity.com/cdnote2.html
Continue the great job your doing with them. They are getting cuter by the day.