Had you put the property into the names of the beneficiaries before it was sold, they would each have had a share of the gain to report of £20,000, the first £11,000 of which would have been exempt from CGT, leaving each of them with a net taxable capital gain of £9,000 on which they would pay CGT at 18%, 28% or a combination of the two rates depending on their respective income levels. Take a look here
for the rules for working out the rate of CGT to be paid by individuals.
As the property was sold whilst it was still an asset of the estate, there is a gain of £80,000 of which the first £11,000 will be exempt from CGT leaving a net taxable gain of £69,000 on which CGT at 28% (£19,320) will be payable on 31 January 2016. Take a look here
for confirmation of the CGT rate paid by personal representatives or trustees. As executor you would need to retain £19,320 to settle the CGT liability.
You will need to call the HMRC Deceased Estate Helpline on 0300(###) ###-####to get a tax return SA900 to report the gain and any estate income (the 2014 form is here
and the 2015 form will be published shortly).
I have heard of cases in the past where the deceased estate sold a property whilst it was still owned by the deceased estate but a letter of intent was sent to each beneficiary before the disposal stating that the property was being sold "on behalf of the beneficiaries to save it being transferred into multiple names" and HMRC accepted that the property had been "sold by the beneficiaries" which enabled them to each claim the annual CGT exemption and to lower the overall CGT liability. Whether this is a possibility in your case, I cannot say.
Some executors have tried to argue that once the estate liabilities have been settled, that they are merely holding the property in a bare trust form for the beneficiaries in which case any gains are those of the beneficiaries and not of the estate. You would need to consult an estate/trust lawyer for a view on that. The wording of the will may be relevant. My own view is that the horse has probably bolted.
I hope this helps but let me know if you have any further questions.