Lower ground floor wetroom waterproofing

[Pari]

I'm creating a wetroom in my lower ground floor. Tight space - extending the WC. So, very narrow and Type C CDM sump-pump not an option. One side is the party wall, that has some damp. The other small wall will be shower area. That had water ingress from the stair cracks above that I've fixed now. Wall is still wet though. Got a few CSSW qualified surveyors to recommend waterproofing options.
Surveyor 1: Proposed putting a membrane used for Type C sump & pump (Newton CDM 503 mesh) clipped and plasterboard with some gap - but without the pump - so used as a Type A barrier for the party wall. And addl. waterproof slurry (Newton Hydrocoat Tanking slurry) + mesh on top in the shower area. When asked where will the damp/ moisture go, he said, it will be so minimal that doesn't need draining.
Surveyor 2: Proposed a waterproof render for both shower and party wall.
Do either of them seem to be a sensible option? I'm no expert, but using only part of sump & pump without drain doesn't sound right...or does he have a point...does it work in some cases? What's the verdict on waterproof render?

 

[Kearn]

Waterproofing / tanking will damage the fabric of the building. It’s as simple as that. It’s an expensive way to do irreversible damage.

Neither of these people is qualified or experienced to go near a traditional building.

wet rooms suit modern houses.

And damaging a party wall is a whole other risk entirely. There’s a simple answer where that moisture will go… next door

 

[Pari]

Membranes are clipped to the wall and can be detached removing plasterboard. But I'm dubious of it without anywhere to drain water. What can I do to have a lower ground floor bathroom then? Next door that area is already an existing bathroom...and they may have already tanked their side.

 

[Kearn]

Pause. Live in the building for some time to fully understand it. And do a lot of reading up on the fundamentals of how traditionally built, solid buildings function.