2 story addition

I purchased a home which was originally a 1.5 story with existing exterior brick chimney and had a home inspection. However, home owner did not disclose a second story was added nor other changes. The home had a 720 sq.ft. full second story addition added all drawings and a permit submitted and approved. Home owner created an in law suit (no permit found). I am now find several issues with the home. Who is at fault as the permit notes "completed" but deficiencies remained outstanding on the date of inspectors initials.

Questions:

How should the brick chimney stack have been built up (frame work, fire blocking etc.)

Floor has too much bounce and support runs to hardwood floor on main floor not through to basement to carry the load.

HVAC does not distribute properly (too cold in winter/too hot in summer)

No cold air return on second floor

Attic relocated from what is noted on drawings and too small an opening (not to code)

Stairs way opening on drawing notes 3' however the construction stairs used, remain in place and the run is longer than original stair case.

Should this responsibility not fall on the city inspector who did not properly inspect the process of construction? Stop work orders, no occupancy until compliance etc.??

Regards,

Desperate for answers