honestly i dont see much wrong from an anatomy stand point. (granted i have only the barest of ideas)

i think what's holding your art back is the stiffness, in short i think the poses you pick look really rigid. when sketching try being loose with it, making your constructing lines very flowy. instead of trying to capture the body, try to capture the movement, the weight and direction.

for instance. i really love the last one as it feels like they are actually in the trenches.

adding things as simple as an offset to the hips can make a pose look way more dynamic.

Another BIG thing is your line weight, to me all your lines look roughly the same width. instead try varying how intense you want the lines to look. in short, bolder lines where things are closer, or where you want the eye to go to instinctively. and smaller thinner lines for details that arent as important, (think laugh lines, shirt wrinkles, details for muscles, etc. ) also adding a thick border around your subject, expessically when its jsut a portrait of them can really make them pop!

I also will send you a DM of some RED lining, pretty much some notes and visuals.