Underplanting established conifers is tricky. Generally the situation is going to be very dry and nutrient poor, due to a dense and aggressive network of tree roots and you need to select plants that thrive under those conditions. The plants you list want far more available soil moisture than is likely going to be available in that location.

Can you let us know where you are located so we can suggest something suitable for dry shade appropriate to your zone?

I am located in Vancouver BC. The area where the cedars are located is actually fairly moist becuase we have an undeveloped forested area right behind us that is very damp. Slugs are a constant demon that I manage with pet friendly pellets.

If the soil remains reasonably moist, then your choices expand :-) Azaleas generally need a fair bit of sun to bloom well so they may not be the best choice but the skimmia and hostas will be fine. Skimmias absolutely NEED shade and like it moist. You can also add ferns (like our western sword fern), sweet box (Sarcococca sp.) and any other shade loving perennials. Another good choice would be Mahonia or one of the dwarf huckleberries (Vaccinium ovatum Scarlet Ovation or 'Thunderbird' or Vaccinium moupinense).

Just be aware that the soil will probably be very rooty, making it hard to dig large planting holes. My suggestion for this type of situation is start with small plants. Easier to dig the holes and smaller plants will establish easier and faster with the inevitable root competition.