Just work on them, it's going to take a while to resolve this and get their feet in fairly good shape.
You have them housed separately, so that's good. You mentioned they won't navigate their ramp. The feet may be a bit painful or it could be the ramp is a little too steep for them. I've...
They have Scaly Leg Mites. As you treat them, that white crusty material will start to slough off.
https://www.backyardchickens.com/articles/treating-scaly-leg-mites-slm-what-you-need-to-know.77376/