CGT/IHT query on property sale

We act for the Executors of an estate, the main asset is a property which has increased by approximately 50% in an 18 month period. The area average has seen an increase nearer to 30% over the same period.

Probate valuations were obtained in 2017 and the value accepted by HMRC. The property was never transferred into the Executors names

It is now approaching the 2 year anniversary of the date of death. IHT clearance has been obtained and we now propose to assent the property to the beneficiaries, who are the adult children of the deceased and who continue to live in the property. The property was marketed by them for sale recently and the agreed sale price is significantly higher than the Executors anticipated.

Once assented to the beneficiaries, they will sell the property as their Principal Residence.

The Executors (not beneficiaries of the estate), are concerned about the significant increase in the value of the property and the extent to which the IHT Clearance Certificate protects them.

What is the likelihood of HMRC opening an investigation into the valuation? Has anyone acted in a similar estate recently?