These covers just aren't working for me, sorry. I'd suggest going to Amazon, finding a bestselling cover design in your genre that you like, and then copying the elements as closely as possible for your story. Get as close as you can with fonts, colors, and sizing. See if that results in an improvement.

The only other course I see open is to hire a designer, and that will probably be cost-prohibitive for an MG SP book, even if it is a series.