I would dismiss the senior management and service management as well as around 50% of the service staff. I would find a thorough training provider. I would ensure before any service user came into the servixe that the staff were fully trained, briefed and prepared to work with this service user. I would not abuse my good staff. I would treat staff fairly and would ensure working hours and work load is fair. The place needs a complete clesrout and restructure. Losing almost all good staff and having to use a lot of agency is a clear sign something is wrong.
To be kind to each other. Take time to chat to everyone ask how they can help and not use there position to bully