Can a payment be made to a deceased beneficiaries estate

I am instructed by the trustees of a QIIP trust set up by a living Settlor in 1999. The trust was assigned the right to receive the future proceeds of a whole of life policy.

From its inception, the terms were to hold the income of the trust for Beneficiaries A & B. Then, after the death of the settlor (triggering the payment of the life policy proceeds into trust), the trustees are given a 2 year window to exercise discretionary powers of appointment of the trust capital in favour of both A & B and also wider family members, in such shares as they see fit. If no such appointment is made, the capital then vests in A & B equally as remaindermen at the end of that 2 year window.

The current issue is that Beneficiary A predeceased the Settlor, and therefore died when he only had a vested right to receive income rather than capital. We are now in the 2 year period and the Trustees would ideally like to pay 50% of the capital proceeds to A’s estate. There is no power to add beneficiaries to the trust nor is there power to appoint capital to the personal representatives of a deceased beneficiary.

My question then is are the Trustees able to exercise their overriding powers in favour of the estate of a beneficiary who otherwise had no vested interest to receive the capital?