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The party who wishes to live in the house can only do so with the consent of the other beneficiaries and Executors. The only alternative to this is if he is actually allowed to do so in the Will, i.e. given the right to occupy the property for a certain period or until he no longer wishes to do so, which does not appear to be the case here.
On a side point, even if you were all in agreement to him moving in and paying rent, this is not a good idea as this might create a type of Tenancy, granting him rights to remain the property and of course therefore make it more difficult to remove him, once the Sale gets near to completion.
I hope this assists and sets out the legal position.