I have experience of this causing permanent family rifts.
Unfair will, disgruntled individual asking beneficiaries to rectify voluntarily, beneficiaries not willing to do so, all parties falling out with each other.
Slightly different circumstances but same result.
My Brother in Law who had had very little to do with his mother and he lives down South.
She used to dread him visiting because she was becoming forgetful and he used to just shout at her if she said something wrong.
He waited until we were on holiday, got the Doctor out and got the necessary letter from the Doctor to gain Power Of Attorney all behind my wife's back.
Within weeks she was in a care home and he asked my Mrs for a meeting.
She thought it was to discuss her long term care needs but it was to buy out my wife's share of her mums house.
She at last saw his true colours and got 3 Estate Agents figures all who came up with the same figure.
She then said she wanted her 50%.
If he hadn't been such a **** she would have given him a substantial discount.
When the m-i-l died during Covid, I sorted out all the IHT forms.
Later in the year he emailed my wife and said he had done all his research and obtained an open market value of his mums property at the time she had transferred it over, enclosing a copy of his Capital Gains Tax liability trying to impress, as he knows that is what I did for a living showing a tax bill of around £15k.
I advised his mum at the time they changed the rules many years ago, to opt the property back in to her Estate for IHT purposes so there was no CGT to pay.
A good half of me thought should I just let him pay it for being such a twat, but my Mrs was under the mistaken impression things would be patched up.
And do you know his beef was all about money.
He is loaded and as we don't have kids we happened to mention our Estate was going to each other, then on the death of the last person, to animal and human charities with legacies to nieces and nephews.
Him and his Mrs took offence that we were putting charities ahead of relatives.
His two kids don't speak to us either even though they were up for £50K each so it just shows how shallow the whole family is and what money does to people.