Girlfriend of tenant refusing to leave property.....

Other

my tenant has contacted me in a bit of a state. His girlfriend who has been living with him for several months with her 10 year old son is refusing to leave our property now their relationship has ended. He has suggested we transfer the tenancy agreement over to her to avoid any further upset between them and he will move out but ideally he wants to stay on at the house and we definately want him to stay as he pays all bills by standing order and doesnt hassle us for anything. The agreement is in his name only so does the girlfriend have the right to stay there because she has a young son and no where else to go?? We havent spoken with her yet but would be grateful for any advise on how we best approach the situation.