Start from a basic pant pattern – mine is with zero ease, so:

• on both front and back drop crotch level by 1 to 1,5cm
• widen crotch by 0,5 to 0,7cm on front and by 1 to 1,5cm on back, redraw crotch curve (notice that on back i filled a bit the curve at back hip – this is to keep center back seam a bit away from body)
• add 0,5 to 0,7cm at front side seam at hip, blending to zero few cm before waist
• add 1 to 2cm at back side seam at hip, blending to zero few cm before waist.

Lastly, widen leg at hemline either by squaring down from crotch point and hip point at side seam, or as I did here by making hem width 3 to 5cm smaller than width at crotch level.

On both front and back, draw waistband parallel to waistline and 4 to 5cm below it. Notice that it is slightly curved on front, and straight on back.

On back, find the mid leg vertical line by folding paper (match inseam and side seam) – most likely you already have this line marked as grainline. Extend this line 5 to 12cm above knee, then draw a quite flat curve ending on side seam 4 to 5cm below waistband line. This line is where the pattern will be split into 2 part – center back and side back.

Now draw the 2 yokes:

• start in center back 4 to 5cm below waistband line with a right angle and curve downward to meet the line separating center back and side back. Meet this line about 8 to 12cm from side seam
• draw a second curved line parallel to the previous and 4 to 5cm below it.

Now trace front separate up to waistband line, measure dart width at waistband line and discard it from side seam as shown from the red line.

Merge the line slowly to side seam, the cut through the new line.

I suggest to mark knee and hip levels with notches.