Gaining Rented Property Possession

Tenancy Types and Management

I’m seeking advice on gaining possession of a large 4-bedroom house that I inherited from my late-Dad.

Background: The house was initially let out in two self-contained flats: a ground floor and an upstairs flat. The upstairs flat was let to a married couple whose tenancy commenced in or around 1986.

In early May 1989, the tenants in the upstairs flat persuaded my elderly Dad to allow them take over and rent the house as a whole, with both parties signing a Protected Shorthold Tenancy (as defined under section 52 of the Housing Act 1980). They were expecting their second child at that time and needed extra space.  In 2003, the tenants signed an Assured Shorthold Tenancy notice and one day later entered into an Assured Shorthold Tenancy agreement.  

Thereafter, the tenants claimed they were protected /regulated tenants  by virtue of them having been living in the same property since before 15 January 1989 and paying rent to a private landlord not living in the same house.  The property was registered for a fair rent as determined by the Rent Officer with this being substantially lower than a market rent.

The tenants separated in or around 2005, with the wife leaving the property and sadly dying a few years later. The husband (remaining tenant) stayed on at the property with one of his grown up children.  After this child left the property, he then took in a young female partner and two children from this relationship. The female partner has been living in the property for a few years now but is not included on any letting agreement for the property.

Letting Agreements:  After my Dad died, I was unable to find a copy of the letting agreement covering the upstairs flat (when the house was previously let out in two flats). The remaining tenant claimed he has a copy of this agreement but he has refused to let me see it.  However, I do have a copy of the two subsequent letting agreements (for the whole house as mentioned above).

 Request for Advice/Guidance:

1. Is the house (as a whole) subject to a protected tenancy or does the latter apply only to the original upstairs flat?
2. I now need possession of my property for an immediate family member of mine to live there. Can this be achieved? 
3. Alternatively, would I be able to retire there in due course even though my late-Dad did not give prior written notice to that effect to the tenants before they moved into the house?
4. Does the tenant’s current female partner have succession rights to a regulated tenancy on this property even though she is not on any tenancy agreement relating to the property?

Any views or relevant experience in these areas would be greatly appreciated.