Application for De Bonis Non Grant or other

Opinions would be appreciated please!
We are acting for Clients (D & E) who will benefit from the proceeds of sale of a dwelling held in trust and which was formerly subject to a life tenancy created in the Will of X. X died appointing A & B as Executors. The life tenancy created in the Will was in favour of C, residual beneficiaries being D & E.
Both A & B predeceased C and without a Grant of Representation to either of their Estates being issued.
C has since died and the residual beneficiaries D & E now wish for the house to be sold in order to receive their legacy.
Question is as B was the second Trustee to pass, would B’s Executor have power to make an Assent to the beneficiaries of the trust property (D & E) by virtue of a Grant of Probate to B’s Will being issued thus enabling D & E to sell the property in their own names or would a Grant De Bonis Non need to be obtained for B given that the trust property hadn’t been administered during her lifetime