The red clay probably needs some amendments to lighten it.
How about ferns? Some of them can really take off and cover large areas within a few years. Best if you have some on the property already and can transplant.
I'm not sure about all the leaf litter that will fall on this area for some of the plants you have listed...seems alot of folks here talk about leaf blowing their vinca and pachysandra,etc.
You might think about first pulling the weeds, adding amendements,then putting down fine wood chips.
Move some ferns into the areas next spring.
Seems like a tricky problem. Ever think about terracing to reduce the slope?

Look into Carex morowii- Japanese Sedge. Some are evergreen, they tolerate shade, damp and dry. They are not vigorous spreaders. There are a lot of Carex out there besides this one.

It will take over and get into any natural areas around it- like ivy does. It won't climb trees and kill them like ivy, but it will smother any natives in the area.

I like the fern idea for at least part of the area.

You might try the _varigated_ vinca minor, intermixed with sweet woodruff.
Pachysandras can intermix with lilies of the valley.

Don't think "groundcovers", think plants for structure and year round interest. Start with ferns and native wildflowers ans some shrubs.