One advice: just start making the full sheet after you've got the first pose done. If you start making the sheet with poor sprites, your sheet will become poor too. I'm glad you brought those sprites there. Redoing one sprite is better than remaking the whole sheet
About the sprites... I suggest working on them before you move onto the animations. Your lineart is good, but can be improved (see 4th guy's shirt, for example. His face is on profile while his shirt is turned a bit to the screen. Avoid making profile faces, unless you can manage them to look good). Another issue is lack of Anti-Aliasing to make your lineart smooth and pleasant for the eyes. for example, see the giant guy's chest, or maybe, the first guy's shirt or the hair from the 5th character. They look like a bunch of lines, and needs fixing. Round these lines a bit more and place the Anti-Aliasing dots on strategic places.
Right now, your colors look strange and boring. See 1st guy's gloves and feet. those are MS Paint default colors, aren't they? You need to avoid using them (unless you're working with some kind of restriction), because they are overall bad for spriting (really, I dare you stare at that light green for 5 minutes. It burns your eyes). About the boring colors... in some sprites (especially the 4th guy's orange shirt), you got one color, edited it to look a bit darker and so on. Making shades is not simple as that: instead, try 'hue-shifting'. Instead of only moving that little arrow up and down on that saturation bar, play with both; move that cursor on the colorful box, too. You may get interesting shades if you do that right.
Also, you need to make more 'fluid' poses. A lot of those looks very stiff and bland. Some look okay, but others doesn't (see the 9th guy. He almost looks like a robot).
I hope this C+C helps you with the sprites. Continue working on these