Here's another photo

Too much water. Looks like you're trees are sitting in a bit of a depression. If you're on clay, you're simply drowning your trees. They also appear to be in your lawn? Not at all a good location for citrus. If they're being hit by your lawn sprinklers, this spell sure demise. They do not like to have constantly wet trunks, as they will develop foot rot (same organism that causes root rot, phytophthora). I would move the trees up into your back bed against the cinder block wall. If you have clay soil, plant them on mounds. Use drip or micro drip watering, and water appropriately so that the trees are moist but not saturated down to about 18-24" deep, which is where the feeder roots reside.

Patty S.