Chimney Removal & Staircase Opening Support

We are converting our loft into a habitable room and the new dormer is almost ready now. However we've reconsidered the original place of the new loft staircase and now we need the front chimney breast disconnected at the loft level (to be removed) and the remaining chimney stack above - supported; as well as calculations and drawing of a new loft staircase opening which will be in the place of the removed chimney.

Attached, you can find more details - hope these explain things better.

Please let me know if you could help.
Look forward to hearing back,