Yes you can. You place up to 12 gemstone dragons, any combination, on your gemstone island at one time. Having one type does not prevent another type from breeding.
No, emerald dragons are not breedable with any dragon. This is true of all of the birthstone dragons.
in order to breed a pearl dragon, you have to be level 10
I was trying to get the emerald dragon by breeding a crystal dragon with a linge dragon. But i got a  dragon
You unlock it at level 11.
Yes, but it was limited edition. It was only available during May of 2012.
There is no such thing as a Birthstone Dragon on DragonVale
The emerald dragon is one of the limited edition birthstone dragons. It was only available during May of 2012. The egg was emerald green. It took 31 hours to incubate, and another 31 hours to hatch. It was bred with a crystal dragon on the left and a lichen dragon on the right.
Earth dragon and plant drago tip go to eggs and look at the dragon you want and underneath the dragon will be 2 sighns so if it is eart and cold bread them in the right order then you will have that dragon ok bye
As of July 2012, there has not been a star dragon in DragonVale.
You don't breed a Kairos Dragon in DragonVale. You have to get parts to complete it.
To date, there is no grass dragon in DragonVale. You may be thinking of the plant dragon. See the related question.
The incubation time for a rainbow dragon in DragonVale is 48 hours.