When you bread with another player and you get twin dragons, which means you get one and the fellow breeder gets the same one. They tend to have a sphere above there head and the egg itself glows as well. What does this mean and is it something special?
It is just appearance differences. According to the Dragonvale FAQ:
Twin Dragons appear differently than other dragons.
The most noticeable difference is a blue orb which hovers above the dragon's head from levels 1 through level 10.
When the dragon is above level 10 the orb, crown, or star will have a blue glow around it.
The buttons viewable from a habitat has a blue background and a yellow glow border instead of the usual gray stone background.
Likewise, when in the description menu the background will be blue and have a yellow glow border instead of the usual tan dragon scale background.
Twin Dragons eggs have a blue glow over them, and if placed on a pedestal the egg pedestal will also receive a blue glow around the egg on it.
So it is indeed different then the level 10+ sphere (sorry for the confusion), but it seems to be only a difference in appearance.