No need to try and get it straight.
Follow the grain and layout your bow.
Do not reduce the width of the handle area at all until you have the bow braced.
Once braced balance the bow with one tip on the ground and the other held loosely in your hand, eyeball where the string wants to sit naturally.
Then simply shape the handle to the string. Eg. if the string goes through the handle area at an angle shape the handle on the same angle.....perfect ly aligned string right through the middle of the handle for a no torque draw
With these sort of staves you can try and get them straight but you will use a good amount of heat, effort, clamps etc with no guarantee that once you brace it everything will 'line up' anyway.