Critique

These are lovely icons! And individually they look great :)
Ahah but like you said as a set they don't look cohesive.
I'll talk about as they are individually first. I like the cutting/blending
for the models. You used some stocks and textures well.
The composition and cropping of the models are good and interesting.
The text you used is very nice and flows well with the individual icons.
Now as a set they don't quite look like they belong together,
there's different color schemes like you mentioned.
Not that all icon sets have to only have one color scheme but
it makes it easier to see that they are together. 
Sometimes multiple or a couple color schemes work well (more with larger sets)
The easiest kind of multiple color scheme set is color + black and white, example below by ghis:

Here's a 2 color + b/w example  by luciana:

And I don't know know what to call this maybe 3 color example by evey:

The last one is the hardest to pull off in my opinion.
But in all these examples, they look like they belong with each other with
more of a reason than just the same model/subject matter.
The first two examples for instance uses similar icon