SDLT Higher Rate for PR on lease extension

I am executor of an estate. The estate’s main asset is a leasehold maisonette, which the deceased had allowed to run down to 42 years left of the term.

I am in the process of extending the lease and selling the property simultaneously. The premium payable for the lease extension is in excess of £40,000, so an SDLT return must be filed. Will I be treated as a trustee for SDLT purposes, such that the higher rates of SDLT apply, or is the buyer considered to be the deceased person/estate, and therefore treated as an individual? If it is the latter, no SDLT will be due, while for the former, there will be tax to pay.