Soil pipe route and length for additional toilet in flat Drainage and wastage systems and plumbing help, advice and answers

[optimistic]

Hi, We live in a tenement block on the fourth floor and I am trying to figure out if we could convert our attic and get another bathroom up there as well as another WC in the flat. I've sketched out a possible plan (see attached) showing where the existing WC and soil vent pipe is and where we want the 2 new WCs to be. Would be grateful for any more info on the following:
1) I suspect the proposed WC in the existing 4th floor flat would have to be a macerator due to joist direction and floor level? Or can you see another way? Height of building and neighbouring buildings means scaffolding up the back to put in a new branch to the SVP externally would be a headache.
2) I have dotted in red a proposed route for a soil pipe from the attic conversion down to the existing bathroom and WC with approximate distances (total 8.8m). Any thoughts on the distance and route of this? Any comments on required fall over this distance? The existing bathroom ceiling is lowered so I'm optimistic that there is space up there to get the necessary fall in.

Thanks very much.