Pelvis animation

Hi, I trying to animate my model with ready pack animations. I successful modded my skeleton to match the ready animations, but I cant fix the pelvis. The original model is taller and has different pelvis bone so my character in idle animation moving his feeds on place, I tried to make each frame one by one but it will cost me weeks for one bone. I have idea how to do this but I will need someone to help me with the math because it is very advance and I haven’t studied it even in the university. I make 3 points - 2 on the toes, one on the heel and the last one - the pelvis, now I have triangle pyramid. My three points on the feeds must to touch the bot plane(they must to have some Z location no matter X or Y location) and then the pelvis will have perfect rotation and I will must to fix the location only, but I cant calculate the angles because I don’t rotate just points across one direction, but it rotating between 2 directions with different potency and I must to find best angles which will make the pyramid to lay on the ground. If you have better idea please share it.

I forget something - my bones is in zero position and has 0 degrees. If I rotate it with 0.5 degrees it will turn with more, but each time when I add 0.5 degrees it will turn less and between 10 and 5000 degrees the rotation effect is around 5 real degrees - like geometric progression. Is here any way to use normal degrees scale for single bone and keep the others with their standard scale?