Make sure they are growing where they should , then if you must move them cut them back and transplant to the happier place.

That would be my advice is watch how much sunlight they receive.

It almost looks like there is landscaping fabric under them -- if so, remove it. Water well and add mulch.

Kris, how old is the house? These camellias are planted in the wrong location wedged between a concrete driveway and a concrete foundation both of which exude lime. Camellias need acid soil and will not tolerate soils with a high pH. There are methods to make soils more acidic but in this situation it would be difficult due to growing location. Hopefully a new home for them is available on your property.

They should be thick and full with virtually no stems or branches visible.....that's the way camellias grow if given the proper growing conditions and the care they prefer. So there is something not right in the growing conditions or they are being malpruned.

Like virtually all other organic mulches, pecan hulls will have NO measurable impact on soil pH. And they are seldom available outside of pecan production areas.

If you live in the PNW, then I doubt you have many pecan hulls or worked with them in the past. I have and they will affect soil pH slightly. Will pecan hulls correct alkaline soil, of course not, Pecan hulls are used for acidic loving plants in conjunction with a landscape plan. The OP can have the soil tested by taking a sample to the local extension center and having it tested for a small fee, And since the house is in the South pecan hulls or pine straw is likely available.

I'm going to diverge from the consensus. The camellias have been severely pruned and thinned but their size and the fact they are flowering where they still can say to me that they are not unhappy with their current growing conditions. You could cut them down near the ground if you want full green blobs. But personally I rather like the gnarly vaguely Japanese or Chinese garden vibe of big old camellia trees showing their structure. I think they just need better pruning.

I think they were heavily pruned because they had been allowed to grow too far over the walk. They will be putting out a lot of growth soon. https://www.americancamellias.com/care-culture-resources/general-culture-requirements/pruning-camellias

How do we know this house in the south?? I don't see where the OP ever indicated a location. And just an FYI but any mulch affecting soil pH is a gardening myth.

I am still concerned that the placement of these shrubs where they are bordered by concrete (house foundation and drive/walkway) will require some ongoing attention to provide a decent growing situation. But a recent pruning would certainly explain their rather sparse appearance. And in that location, pruning in the manner to which floral referred is certainly appropriate.....otherwise they are just going to overwhelm that planting area again in the not too distant future!

At a previous home in San Diego, I had a 50-year old camellia bush planted up against a concrete block wall and a sidewalk that stopped very near the base. It was on the north side of the wall, with a tall house behind the wall creating deep shade. That thing was huge and dense with leaves and flowers. I trimmed it once to "lace" it -- allow more light into the interior of the plant. It grew doubly fast after that, quickly filling in all the blank spaces.

If these were mine, I would bring the height down somewhat and allow them to fill out laterally. They may have been pruned this way because they are in front of windows? A solid shrub is not a good view from indoors. Not the best placement, but that could explain the way they are trimmed.

I think they were butchered. In my experience with butchered camellias in CA, they'll be back.

(That reminds me, I need to go butcher my camellias again. My front room is getting very DARK.)