I'm not sure what exactly you mean by "relative to the camera". You can translate objects by using, well...translate(). If that has to happen relative to the camera, you have to calculate the new position based on the position of the camera by simply adding it and then do something like
obj.clearTranslation();
obj.translate(newPosition);
If you don't clear the translation in the case, the translations will add up.
To answer your second question: Yes!