They also haven't been going out too often, so even though there were also a lot of zombies in farther areas, they probably hadn't experienced too much trouble from those, as they weren't seeing them often, so they were still able to maintain a good mindset.
And according to Ferman's son, wherever they go out, they were always cautious and would mostly avoid contact with other people unless they were already a bit familiar with them and had seen that they weren't a threat to them.
They were also often using safer routes and would always find a way to avoid confronting zombies. For example, if they needed to go to the next building or to the upper floor, they would often use ropes and other things and wouldn't use the first floor, which obviously had more zombies from outside and other places, that's why they had always managed to return.
They actually also had mice and were using those to check if their water and food would be safe for consumption.
