Hi, I'm new to mice and I am trying to introduce a new mouse to a pair. I've got them in neutral territory with just a bit of food and a tube. They aren't fighting, but the two established mice seem concerned with nothing but escaping the box. The more timid (largest, likely oldest) one especially is just constantly jumping up the sides trying to escape. The younger one is more chill, had had a couple seeds, is in the tube with the new one sometimes. There's not a whole lot of interaction going on between the them and new mouse. Do I just wait it out, add or remove something, introduce one mouse at a time....? Please advise.