Yes of course, but the reason only they could find it out is also that Minerva needed to hide this pen. If it was obvious then the risk of the Demons finding out would be too high. I agree that only the strongest can make it. Finding an easy route is not something that can be done just like that but I'd imagine that even the stupid kids wouldn't take the dangerous route because the way they are taking just screams death and they do have a map after all even though it's not very detailed. A weak group would never make it out that's for sure but it doesn't necessarily mean that Minerva wants only the strong. A strong group can also have weak members.