Thanks for your enquiry.
If no new Will is made, then the Executor is under a duty to comply with the terms of the existing Will.
However, provided all the beneficiaries under the existing Will are happy that the terms of the Will be changed, in accordance with your Father in law's oral wishes, then a Deed of Variation can be prepared after your Father in law has passed on, which acts as a variation to the existing Will, and then your Husband, as Executor, can then distribute the Estate in line with the Deed of Variation.
A local Wills Solicitor can assist in preparing the Deed of Variation at an approximate cost of £250 plus VAT.
I hope this answers your question, and if so, I would be grateful if you could leave positive feedback.