You have problems.
You will need to get either an architect or an engineer, as you had an architect, I would suggest an architect, who is prepared to to a comprehensive report detailing the current problems and the causes, pinning blame on either architect who supervised or the builder or both.
Another problem, is are both insured? If one is not, then if at the end of the day a Court was to decide against that person or persons, how would you collect? Are they both sole traders, or limited companies? If sole traders, you can go after personal assets, if a limited company, you cannot. Is the architect a member of the RIAI?