Thank you for your question
My name is Clare
I shall do my best to help you but I need some further informtaion first.
Are you also the Executors of your late father's Will?
Who dealt with Probate for you - did they not take any action regarding the house
But you did get the Grant?
This is an interesting area of law (for which read complicated)
Because of the way Land Law works his partner is now the sole Legal Owner - but she holds it on Trust for herself and you and your sister.
You and your sister as Executors can certainly prepare an AS1 regarding the property assenting to the Transfer into all three names - BUT the partner does not have to agree.
However doing this will make it easier when she wishes to sell the property.
You remain protected in any event - but it would be sensible to make contact and try and resolve this.
Please ask if you need further details
Have you checked the Land Registry and downloaded an up to date copy of the Register Entries?
Who owns the property - set out in the Proprietorship part of the Register
Well that confirms that at present all is well and the property is still in joint names and the restriction on the Register means that she would have to appoint a new Trustee f she wished to sell the property
If your attempts to get her to sign an AS1 fail then you can apply for a further restriction to be entered on the Register to confirm that you are notified of any attempt to dispose of the property
You are most welcome I hope all goes well