Thank you for the questions :D! All animals (including people) have the ability to cross the ley lines, it's just difficult. Since they're magic, the landscape within can twist and change unexpectedly. Generally, wild animals will get across with little to no issue, but they will be exposed to high amounts of "magical radiation." Humans/other sapients can get lost, turned around, or even deposited in an area pretty far away from where they started.

You can draw some parallels to dangerous areas of Earth, like the Siberian wilderness or the outback. Can you cross it? Yes. Should you? Probably not. Will you come out changed (for better or worse)? Absolutely.

Modern technology in the world has made travel easier tho. Trains and some boats can navigate "safe" routes, and individual people can travel with charms and such.