How do I remove two people from a house?

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My family has had a house left to us in my fathers will. He died in November last year. Our intention is to sell the house. There are two people living in the house with no contract and are not paying any rent. We have asked them to leave and given them two months official notice on top of the ten months that they've known that the house would eventually be sold.

Their solicitor has written to ours stating that they intend to stay until the house is sold but our solicitor/estate agent is reluctant to market the house with them in it because if it gets sold and they still refuse to leave, its going to cause us even more problems.

As far as I know they have no rights as there is no contract and their not paying rent. Is this correct?

What is quickest and easiest way to get them out of the house?

Thanks.