For the cover of book 1, I knew exactly what I wanted. I wanted the wavy header, I wanted to see the title in white, I had a say in the overall coloring of the book cover and even various little details on the boys, themselves.
With the covers of books 2, 3, and 4 - I did the best I could with what I could find. I purchased royalty free pictures and dropped in the text. Now - I do like those covers, but they are not the same as book 1. Therein lies the problem. In creating a BRAND or product recognition, people need to know what they're buying and that it's all related. But I simply don't have the artistic ability to create something similar, myself. So I may look into what a cover illustrator would charge me to create original book covers for the rest of my series.
I'll let you know what happens and how that works.