It is not possible to reinstate a previous will. That is because a new will revoked the will. It would be necessary to do a new will.
If your mother had simply destroyed the will leaving everything to her partner, then she would have died intestate and everything would have gone to her children. That would have solved the issue.
As it is, there is a perfectly valid legal will it seems albeit that the terms are out of date.
Family and dependents who have been cut out of the will can bring a claim under the Inheritance Provision for Family and Dependents Act.
A claim for that, in the circumstances will succeed but it’s unlikely to succeed in overturning the whole will.
Can I clarify anything for you?
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