Tenant & Landlord Contracts?

As a rental agent in the US I may be on shaky ground, as you are in the UK, but here we have online services that can check out the credit and tenancy history of prospects. The services are available to landlords for 30 to 50 dollars. You can save the estate agent cost, and can charge the prospect for the cost of the service. The only possible danger is that your mum and dad would be exposed to an unknown person at the home each time they met another prospect.