Tied or Assured Tennant?

[janbreed]

I moved into a small chalet type accommodation on a farm March 1997. The farm owner stated that in return for 2 - 3 hours light farm maintence per week I could live there rent free, electricity and water included. When he retired I was ask to say on as caretaker/manager. There is no written agreement or contract.
I have maintained the property including replacing the windows at my own expense. I pay a small rent to keep my horses here, and was allowed to make hay as long as I paid all the expenses incurred.
The farm owner died last week, his family have already been quite intimidating.
I would like to stay in situ if possible, if not, are the inheritors obliged to find like for like accomodation as I have invested time and money into now their property?
What are my rights?