With regards to the models it is likely they would be regarded as if employees in a legal case, even if contracted rather than directly employed.
The employer has a duty of care towards its employees and will need to be able to evidence that it has taken appropriate steps to minimise health and safety risks wherever practicable, for example:
(a) Vetting all clients thoroughly beforehand, perhaps keeping scanned copy of passport, driving licence or other photo ID;
(b) Risk assess and authorise specific locations beforehand, taking into account a number of safety factors, such as mobile phone networks signal strength, driving time from nearest Police station, driving time from nearest Taxi company/stand, fire risk (suitable smoke sensors and fire control panel installed?), carbon monoxide risk (gas appliances regularly checked and certified as safe?), electrical safety (wiring certified safe by approved electrician), suitable temperatures, etc.;
(c) Vetting and authorising specific companies used for protecting/transporting models to and from the locations of their clients;
(d) Rather than simply getting them to accept terms and conditions, educate both clients and models on what is and isn't acceptable and ensure they have understood why (e.g. specific laws that apply, or the rationale behind the rules);
(e) Prepare incident response plans undesirable scenarios;
(f) Establish a confidential protocol for periodically checking models are OK, for example they must call in or send an SMS message to a central monitoring system where someone keeps track of activity and movements (I would also advise deleting the message from sent messages immediately after to help keep the protocol confidentidal);
(g) an emergency hotline for models to report 'red flags', such as inappropriate behaviour/expectations, unexpected changes to schedules/locations;
(h) Obtain specialist insurance for the risks and liabilities of this business;
(i) Obtain specialist legal advice for any other areas of risk/compliance that need to be addressed, and establish a working relationship with a legal professional who is prepared to step in and help you if/when trouble arises. It might even just involve a monthly phone call to just keep them aware of any new risks and actions taken, and to let them know of any potential issues so they can advise, and they can keep you informed of legislation changes and help you keep compliant. They can help ensure your terms and conditions provide the maximum legal protection they can.