Dad's Ex-girlfriend asking for too much

[Totemoneru]

We are in a horrible probate process with my late father's house and wondering if anyone can help with advice.

He owned a house which he has left in an equal split to his surviving wife and children. Everyone is happy with the situation.
However...
One of his children was by a girlfriend he had before his wife.
She left him for another man. It was tough on my dad. She's not the smartest of women and had always struggled a bit with her mental aptitude. She is now quite poorly and has dementia.
When she left, her then boyfriend suggested she put a caution on my dad's house for a fixed amount. She says she paid into the mortgage however she never did. She had a council flat paid for by benefits whilst they were in a relationship. They never married, they never lived together. This was 20 years ago.
My dad was advised (poorly by a solicitor "friend") to just pay what she was asking and include it in his will as it's be costly to challenge it.
Now we are hearing that they will not remove the caution and are demanding that on top of the fixed amount, they have 20 years of interest and all their legal fees paid too before removing it.
The useless solicitor handling the probate (my step mother has insisted it be this friend of hers and as she is executor we can do nothing about her choice) is just saying we have to agree to it all.

This seems ridiculous to me. The ex girlfriend has absolutely no evidence supporting her claim that she contributed to the house. She also has dementia so it's her daughter calling all the shots.

Do we really have no legal recourse here?

Of course you have legal recourse it’s a caution not a charge.

What exactly did your father state in his will about this?

They are asking a lot. Tot up the costs of an actual solicitor worth their salt and compare the value.

That isn't right. What you need to do is to provide proof to Land Registry that the debt stated on the charge has been paid off and complete form DS2.

https://www.gov.uk/government/publications/cancel-entries-relating-to-a-charge-registration-ds2

The Land Registry will then remove the charge

His will states that she is to be paid £12,000 due to her contributions to the mortgage repayments.

He was extremely angry at this being included and said he didn't want it in there but his solicitor friend urged him to just pay it as it'd be cheaper than fighting it.

When we (kids) found out we reassured him he could change it and we'd organise changing the will but unfortunately he deteriorated very quickly and ran out of time.

Our solicitor is saying that because it is an old caution (2008) that it can't have the caution removed. Only his Ex-girlfriend can do that with a solicitor of their own.

I can't understand how any of it is being paid without some kind of proof of payment made by her.

That doesn't seem to make any sense at all. The age of the caution has no bearing on things at all. If the debt referred to on the deeds has been paid off then there is no need for the charge to remain.

Perhaps suggest to your solicitor that you make an application to the County Court for an order discharging the caution. Again, you will need to show proof that the debt has been paid off.

Also, perhaps speak to another solicitor.

I doubt you have a leg to stand on in saying your late father doesn’t agree to the £12k.

It’s not the £12k she’s objecting to, I think: it’s the + 20 years of interest and legal fees on top.

Yes it's this.
I know we have no legal to stand on when his friend convinced him to leave it in his will. He was livid but felt powerless. It's infuriating that bad advice made that happen. However we are aware this looks like an admission.
It's the holding the house sale up to ransom and knowing my father would be turning in his grave that is upsetting everyone.