Half finished House Extension plans need completing

Unfortunately a family member who offered to undertake some house extension plans (under PPA) has let us down having only done the very basics for us.

We are looking for someone to finish the plans, which involves a significant amount of internal restructuring and removal of internal walls (none are load bearing) and also advise us on drainage and placement of utilities that require drainage based on our requirements and advise on structural aspects due to us wishing to remove a lot of internal and external walls?

I have attached a copy of the original CAD drawing done by my relative with all the amendments I required added to it.

We are still looking at applying for Building Regulations at this stage unless advised otherwise.

Thanks

Karen