Answer: Technically speaking you can prune rhododendrons back hard and they will develop new growth. In my experience, this works most reliably if the plants are strong and growing well. If plants are weak and cut back hard, they might not recover.
My advice is to cut back a little and see what happens. Remove to its base one of the lopsided branches that's bothering you and see how the plant responds. Obviously, this means you'll need two or more seasons to prune all the rhododendrons into the shape and size you want.
Do you like the plants? I ask because another alternative is to be more drastic. . .cut them back and see what happens. If you kill them, you can replace them with similar shrubs.
The best time to prune rhododendrons is just before their major push of spring growth. I'm not sure exactly when that is where you live, but if the plants show a lot of new growth, it's too late.
In the meantime (if you want to save the plants) do what you can to improve conditions: water (as needed), mulch, fertilize (according to package directions).
And I think the conditions under the pines might pose too much of a challenge for the Rose of Sharon. The pines' roots compete with the shrub, and the needles make the soil more acidic than this plant likes.
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