Get them dressed in what you want them to wear in the picture, take them to the studio and let the photogropher do the rest. They have the experience. You don't have to say much to the children other than we're going to have our picture taken. Thats it.You don't need to prepare them, that will just get them all 'jacked up'
Bring extra clothes just in case they make a mess on themselves some how. Oh and if you have a good photographer they will make sure to catch the attention of your boys so they can snap some good pictures.
What kind of photographer.. someone who sits the kids down and tries to get them to smile or one that does snaps pictures of them playing and being themselves?
I recommend going with the simplest outfit possible.. the less color and distractions from the boys face.
