There is much much more management can do beyond speaking to the GP.
They can consider increased staffing including 1:1
They can ask the local older adults mental health team to review and look at OT, strategies, medication etc
They can identify that it's no longer the correct setting and request a review from whoever is funding.
If there are unmet dementia nursing needs they can request a nursing assessment with a view to a move or an increase in nursing staff.
They can put keypads on any areas where it would be dangerous for confused residents to access
They could increase activities during the day so people are occupied rather than wandering
They could train ALL their staff including kitchen, admin and domiciliary staff in dignity in care and in dementia, as well as basic breakaway techniques. All staff should also have received training in whistleblowing and safeguarding adults from abuse or neglect.
Regular staff meetings where open conversation identifying concerns and discussions about what the managers are planning to do about the concerns.
If staff are being assaulted then they are absolutely entitled to report it to the police as well. Nothing will happen from a police /criminal perspective but there is liaison between police, adults social care etc and if something awful happens it all gives a clearer picture for prosecution etc if managers were aware of risks and didn't do anything about it.