If the Aunt died domiciled in the Isles of Man, would it not be the Manx law and legislation which would apply to her estate, and not the English jurisdiction?
I am assuming perhaps mistakenly that the assets she left in residue are in the IoM, but even if not, there may need to be a variation in the IoM even over UK situs assets.
If the deceased husband has not appropriated the property, in one way of another, it might remain outside his estate as such, and might escape the widow’s ability to vary the aunt’s will on that basis.
Perhaps best to start from the IoM with assistance from a Manx lawyer and then work forwards to see whether the Husband or his estate has actually been seized of the property under Manx law?
That way there would be no question of the widow using up her UK advantages, merely any as may be available to the Aunt.
Peter Harris