departing tenants

Tenancy Types and Management

two of my tenants have just informed me that they are leaving (2 days before their section 21 expires and im just about to issue proceedings) i have a couple of questions and would appreciate any response

1) would the handing back of both sets of keys be suffice to say that their occupation has ended or should i ask them to sign something?

2) only one days notice was given of their departure when i have always stipulated 2 weeks - i think i will let this go as im glad to see the back of them after the trouble they have caused and they said they would clean prior to departure!