Some additional photos.

Seems like a waste. I'd dig them up and put them in pots until they recover.

how much work are you willing to put in?

Citrus will do fine in clay. What is the pH of your soil and water? Citrus don't absorb some minerals well if the pH is over 7.5. My first thought is you ought to at least double the water. What rootstock are they on? Some are more susceptible to phytophera than others. Where would the phytophera come from? Most commonly it comes from surface water like rivers/floods/etc; and for it to affect your tree, they normally have to be completely saturated for some time. If you only fertilized 3 weeks ago, you might just need to have a little patience.

I agree with John, I was also going to suggest more water, maybe the same amount but once a week instead of every two weeks. It is very hard to over water in ground citrus, even in clay, unless you're watering multiple times per week or day.

Evan

I agree with Evan and John on all their advice. I think they are nitrogen starved and lacking water.

Clay soil is full of lots of mineral nutrients and in CA we rarely have to add phosphorus or potassium, in fact it's not recommended to add phosphorus as it can be too much for most CA soils since there is plenty there already.

However, it's almost always lacking Nitrogen. And your trees show classic nitrogen deficiency. Even though your fertilizer is for citrus, 8 is pretty low for nitrogen, at least for in the ground. At that level though you can safely feed monthly, which you may need to do.

That amount of water was probably fine when it was cooler but as we are rapidly warming up all through the state, you need to up your irrigation frequency also.

Unless you are watering everyday in summer, you most likely will not have root rot issues. But if you just want to be sure, get some Agri-Fos. It's the best product to combat Phytopthora. You can get it at most good garden centers. Usually once or twice a year is good, but of course always read the label. I've had good luck with it on two very old orange trees with chronic gumosis. It's stopped the progression and holds it at bay, and they've actually grown new bark and more canopy since I've been using the Agri-fos twice a year.

One last thing, (sorry for the wall of text) the holes and chewed spots look like you may have had an Orange Dog Caterpillar at some time. It's pretty much the only pest that eats citrus leaves. As your trees get bigger the caterpillar is not much of a threat, but they can be hard on young trees.

Thanks all for the feedback.

Likely your soil pH is alkaline or nearly so. Get a professional lab test and tell them you want recommendations for growing home garden citrus.

You may need to use chelated iron. But wait for the recommendations from the soil lab.