Notice to leave from tenant but refusing to go

Other

My tenants (boyfriend and girlfriend) have split up. 

Boyfriend has given notice to leave the property and is therefore due out soon, I am aware this applies to them both as joint tenancy.

I cannot agree terms with the girlfriend as she has no income and poor credit so therefore I have responded to say I accept the notice and they are due to vacate. 

She has now told me the council has told her (and her 2 children) not to leave so she wont be going anyway. 

I need to be sure what to do next so I am ready, if anyone has any experience on what that is (quickest way) and how long it is likely to take it would be much appreciated.