In my scene I added 3D models and I attributed the mesh collider and the rigidbody.
When the player hits a model collisions there are, but if there are two models to touch, they go through, they seem to ghosts.
How come there are no collisions between a model and the other?
One of your two mesh colliders must be marked at Convex in the collider component. And for Convex to work, there must be less than 255 triangles in the mesh.
Simply add a rigidbody and polygon collider to each model-or, if you want, a box collider. Get rid of the mesh collider. I think this should work.