IHT - Issue with parents property

My father passed away in April Mum still lives in the house they shared but they were divorced at the time. They bought some land surrounding the property in 2012 but it appears the Title for the land did not get transferred into their names. The solicitors dealing with it at the time dropped the ball and have since ceased trading. The council had some queries at the time so the transfer did not complete. So we are in the position of trying to value the property for IHT purposes as he has left this to me and my daughter (Mum has living interest). The value with or without this extra land makes a big difference to the value of the property for IHT. We have contacted the land owners and they are saying they did not receive the monies for the land so it could take a while to sort out. What do I do regarding probate in this situation?

Hi,
Please contact the Inheritance Tax team for advice.
Inheritance Tax: general enquiries
Thank you.