Its always hard to tell from a photo, but this may be camellia japonica 'Governor Mouton' a classic older variety that originated in Louisiana in the early 1900s.

I still think it is camellia scale, which affects the lower part of leaves and slowly causes leaves to turn yellow. But, here is another possibility... you may be suffering from cottony cushion scale. Its symptoms include "cotton-like" spots on the leaves and joints of the branches. If their numbers are small, you can swab them off with an insecticidal soap or alcohol-dipped cotton swab. If the numbers are too high, then you need to turn to a systemic insecticide, which is potent and has collateral effects on some plants. See Figure 26 in the link below. If you could post a picture, that might help. Luis Here is a link that might be useful: Cottony Cushion Scale

Generally , I've not had any problems getting blooms with just some supplemental feedings of an "iron" fertilizer, but is it possible they're in deep shade during the summer? They do like shade , but I'd think "dense" or low shade might be a bit too dark to encourage blooms possibly. Also , I bought a small cutting grown plant and it bloomed the next year, so it wasn't terribly old nor do they have to be usually to start blooming from cutting grown plants, but it's possible though not likely it's a 'seed grown" one. And those could take much longer to bloom.

Thanks for including us:)