I have just inherited my parents’ house since both have died

I have just inherited my parents’ house since both have died in the last 18 months. I have just sold it subject to completion. Unbeknown to me the executors sold it for me to give me the proceeds. The valuation they gave probate was for £590,000 but the house has sold for £810,000, hence there is a capital gains tax charge of between of £50-60,000 on the uplift. Leaving aside the completely erroneous valuation I was not too worried since I had intended to give a sizeable church to charity, and was hoping that the charities would be able to reclaim the CGT that had been paid. But the trouble is that whilst I effectively pay the tax, since the sum passed on has had the tax removed, I am not sure I can sign a GiftAid declaration since it was not me who sold the house, but the executors. Can I still enable the beneficiaries to reclaim the CGT?
JA: Where are you? It matters because laws vary by location.
Customer: UK
JA: What steps have you taken so far?
Customer: None, I am awaiting the probate which will come through when the house sale is completed.
JA: Is there anything else the Lawyer should know before I connect you? Rest assured that they'll be able to help you.
Customer: No