Consistency in illustration style

I'm struggling to keep the style consistent in my pencil illustrations for my juvenile novel Kiddo, due out this spring. The drawings done in numerous sketchbooks, usually on the bus or other locations where I have to wait for appointments or otherwise put in time are all stylistically different. Illustrations where I'm dependent on photo references are particularly problematic.  Then refining the scanned sketches in photoshop produces another style variation because digital pencil isn't the same as real pencil on paper.  Tracing sketches has always produced a lifeless result for me, so photoshop seems like marginally better option. Fingers crossed it will come together in the end.

Pop sculpting alien. Sketchbook drawing with no photo reference or photoshop. I wish I could do all the illustrations in this style. But there's a problem: Pop's motto is "safety first." I'm sure he wouldn't use a tiny welding mask like this, especially with his whiskers. But I like the drawing of his face.  Maybe I should try to reproduce this face in another illustration of Pop and put the full mask on this one.

Kiddo carrying Dwarf Star, a lovable, but very heavy baby. No photo ref for first sketch. The 2nd drawing shows a lot of cleaning and redrawing in photoshop. But it feels over-refined compared to the Pop Welding image at top.

Kiddo confides in Pop while he fixes the sink. No photo ref except for the p-trap pipe under the sink. very messy sketch with quick cleanup in photoshop. Need to redraw either by tracing over in photoshop, or with tracing paper.

Kiddo and Winston on the run. Mostly done out of my head with a reference for the dog. Did an experiment of drawing with blue and red Col-erase pencils, then overdrawing with 2B mechanical pencil. But was unable to cleanly remove Col-erase in photoshop without losing a lot of good pencil overdrawing.

Kiddo putting on roller skates. Heavily reliant on a photo reference and it shows, especially in the face. 

Kiddo and Winston. No photo ref, style is messy, but too idiosyncratic to trace. A case of getting it right by accident which is what usually happens to me. Plus each head is drawn with a different pencil: Winston was done with a 2B mechanical pencil and Kiddo drawn with a wooden 3B. They were on different pages of my sketchbook and I combined them in photoshop. I wish all the illustrations were messy like this or all clean like Pop Welding. Ideally, nothing would be done with close reference to a photo, but there's too many things I need references for. So frustrating.