I love rats. They are Intelligent and friendly. Did they tell you the rats were 2 mnths old? If so, they are not used to being handled yet. It will just take some time to gain their trust. At a pet store they could have been mishandled by people visiting the store. You just need to be patient. You also need to realize they were never given treats at the store. So other than the food they were eating, (lab blocks?), they aren't used to other things in their diet. I used a little cheese...
I'm so glad you chose 2 females. I always had 2 females, or a mother daughter. Never had a fight like males can have.
Just give them time, take them out together, give them a place to hide in their home. They sell these domes where they can make a nest. You just talk to them and lift it when you get ready to take them out.
When you do take them out, get o the coach with a blanket. They love to crawl between the covers and play.
Rats do not usually poop when they are out, so you're right, they are still frightened. However know that rats do wet sometimes when they are out, they do not have good bladder control.
After awhile you'll be enjoying them and they will make you glad you chose them. Good luck.