Pretty rough, but simple:
leftLeg.x = torso.mcLeg2.x + torso.x - leftLeg.mcTorso.x leftLeg.y = torso.mcLeg2.y + torso.y - leftLeg.mcTorso.y
That means the X coordinates of the leg will be the result of the X coords of the leg joint in the torso, plus the X coords of the torso related to the whole stage, minus the X coords of the torso joint in the leg.
Same thing to the Y.
It’s actually easier than it sounds to be…