The council is powerful, with both legislative and executive authority. The mayor is not truly the chief executive, with limited power or no veto power. The council can prevent the mayor from effectively supervising city administration.
The builder is at fault, however if there is no legal document that he has signed to say that he would complete the work and help them, then he isn’t liable.
The act/agency that makes regular surprise inspections to ensure businesses maintain safe working environments is called the Occupational Safety and Health Administration.