Carolina,
The plants are all planted so close together, I can hardly see the plants you are concerned about.
The purple flowering plants with the darker foliage is the heliotrope, right?
Mabey take some plants out, and give them a little more space between the plants, they are all squished together too much.
What kind of tree are they planted under?
Usually I water my plants a little more if they have to compete with a tree for water especially in warmer weather.
yellowing USUALLY means a water problem.
Either too much, or too little.
Not all the time, but usually.
Stick your finger down in the soil where the roots are on the plants you are concerned with and see if they are moist. If not, water.
Good luck to you, I hope they pull through and grow nice.

This plant requires full sun, wind movement, and lots of fertilizer.

Butterfly made a great point. They are too close rot other plants being robbed of fertilizer , and moisture. The ugly part is this. Because the other plants are robbing the roots of moisture , you have to water more often which in turn causes boytritis. This plant is very prone to this if there is a lack of air movement. , full hot sun and or leaves getting wet too often.

Remove the plants around them or dig them up and grow them in pots and they should come back

Butterfly, hello",

Mike

Thanks, guys! I actually cut back on my watering, and they have been looking very good. I even saw buds on one. :):):)