Hmmm. Their bellies definitely aren't white. You can see the pattern in my profile pic..although not well. They don't look like streaks though..but diamond shapes that got squished. Yoshi, our skittish dragon does have the streaks going down her neck..but she is super skittish still and hisses etc. We're working with her to create as calm an environment as possible and even put newspaper all around the cage which has helped her feel closed in and secure (so it seems). She's not seeing her own reflection anymore at least. Timba is very calm, hardly any streaks on his chin, but a very patterned belly. We've had them both about 2 months.
They don't always look like 'streaks'. They are commonly oval'ish patterns on their bellies, sometimes having streaks connecting the pattern together. Sorry if I am a little behind here, but are these two housed together? Can they see each other if they are not? What are your temps and how are you measuring them? Their light/dark cycle? This will help us get a start on why they have those streaks. Some will lead you to believe that it can be 'normal' on some dragons, but the likelyhood of it being on both is very unlikely and more likely to be something going on in the environment. Possibly even the room they are in.