Keeping half a chimney stack

[9treesway]

Hi all, looking for some advice on a shared chimney stack.

We just purchased our terraced home and the survey found that the chimney breasts had been removed and the stack supported with a rubbish gallows bracket that has collapsed. The stack is currently resting on the ceiling of one room (so yeah, very dangerous). We've approached the neighbour in person and via a party wall surveyor about removing the full stack which our structural engineer heavily recommended, but the neighbours want to keep their half which means we have to pay to make sure their side is secure. I didn't even know you could keep half a shared stack! Anyway, some questions:

1) Who do you even ask about how to proceed with this? Do you get the roofer to do the work then a structural engineer to certify that their side is structurally sound?
2) Can they even make keeping half the chimney a requirement when it may be too narrow and potentially unsafe?
3) If they insist, and in the future it falls or shows signs of damage, would we be responsible for costs to fix?
4) They are unable to give the party wall surveyor (or anyone) access to the loft on their side as they removed the hatch a while ago. This means we have no idea of the condition of their side of the wall or the bracket that they say they have supporting their stack (their chimney breasts were also removed a while ago). If their half of the chimney stack falls or shows damage in the future, would we be responsible, despite not knowing the condition of their side before work was carried out?

Thanks in advance!

 

[Laurieo]

Sounds like they have something growing in the loft space

 

[cdbe]

Plenty where I live they've just literally sliced the stack vertically down the middle (well obviously offset from the middle) and flashed and rendered the leftover mess. Try to avoid party wall nonsense, treat it as an urgent repair and get builder with roofing experience or a roofer with building experience up there.