How long have you had them? Can you describe the behaviors that you are seeing? Is one more confident than the other? I've adopted rats from the shelter before, but they ended up being very friendly after giving them some time to adjust. It was actually a rat that I got from a "breeder" that showed intense wariness of people. I recommend just giving them time to get used to you if they are relatively new. If they clearly need some bmod (behavior modification) then there are tons of different techniques you can try, but, again, give them some time to settle. Even just classically conditioning a sound could help (essentially teach a recall using a soft bell, tongue clicking, or other). Counter conditioning handling is popular, but I really enjoy operant conditioning for bmod such as targeting or jumping into a hand. If they are too scared to even do any training with you, then counter conditioning is useful but it works best if your timing and stimulus presentation is immaculate. I am happy to elaborate on any of these techniques if needed.