repotting cactus?

Fire

This cactus of a friend is poorly. Could I get some advice on repotting, soil medium and general improvement of health?  Thanks

Fire

Thanks

Joy*

If you put them outside, beware of them having too much sun. I thought that desert plants would like it but caused one of my prize specimens to develop a corky layer on the surface. I did everything I could to try to get it going again but sadly it didn't make it.