Stratafied – I’d advise ascertaining the Engineer’s details including their qualifications, professional affiliations, the nature and extent of their liability / professional indemnity cover, the terms of their appointment including the scope-of-work that was provided by the Owners Corporation (Executive Committee and/or Strata Manager), and the text of what was actually reported by them.
If you’re unable to readily obtain that information such as where the Executive Committee prevaricates, and you’re in NSW, then make an application under S108 of the NSW Strata Schemes Management Act (1996) and provide your Strata Manager with concurrent advice about precisely what records you want to be made available for inspection.
Once you have that information, you and the other Owners will be in a position to better determine the extent of any professional negligence, and will also know from whom and by what process the Owners Corporation may best seek recompense.
I hope it’s not the situation in your case, but I have personal experience with clients such as your Owners Corporation seeking advice from inappropriately qualified and/or less experienced consultants, with either no scope-of-work or with one that’s driven more by a budget than it is by what’s really required.
Anyway, at least the suggested approach should guide you and the others in how hard to push and in whose direction!