Nice trial. It seems to me that you are drawing with your hands using chicken scratching method. The line quantity can be improved with time and while doing exercises to draw from your shoulder or elbow. Like drawing planes and try to execute the ellipse inside it while using your shoulder. I suggest you try Drawabox lessons and exercises for it. It will also help you understand how to construct and make objects look more 3D. That's another issue I see here. Also you can vary line thickness. Making the lines for the planes facing the viewer a bit thicker or heavier than the ones in the back will help selling the illusion of dimensions. (Which is also explained and have excercises for in drawabox). You did well in the first pelvis, but the rest are flattened out (probably due to angles as well). Have a great practice day :)👍🏼