Except for the Rhododendron, all are quite happy in full sun. Their lack of vigor is most likely due to unfavorable soil conditions and possibly insufficient summer irrigation. I'd move the rhodo to a more shady position (afternoon shade at least) and topdress the area with several inches of compost. If you do this on a routine basis - say annually - eventually your soil conditions will improve and you should notice improved performance. Ideally, soil improvement/amendment should be done to an entire planting area before planting. Make sure you provide deep irrigation during dry periods.

Gardengal said it very well; although I suspect poor soil is a major problem. You can speed up improving the soil by digging a 6" deep [and ditto wide] trench just beyond the dripline; fill it with compost and then put 2 to 4" shredded leaves as a mulch over the trench and up to a ring about 6" from trunk. Use coarse gravel as a mulch between the leaf-mulch and the trunk (that deters nibbling critters). Check every few months because the leaves will gradually decompose and more should be spread on top.

One way to determine sufficient water is to plan to irrigate any time you don't get 1 inch rain in 10 days (if they are baby plants, figure 1" per week). Water slowly to give it a chance to sink in rather than run off. Shrubblers, soaker hose, gardeners-IV bags, even a tiny hole in the bottom of a large bucket are any and all better than turning the hose on full-blast.

The rhodie will do best in part-shade and a soil that is full of humus and fairly well-drained. It will also probably sulk for a year (they don't like being moved) but then take off to reward you with a gorgeous display of blossoms.

Thank you. I will try that! :-)