I am of the view that the will should be administered in accordance with its terms – a one third share to each beneficiary.
The will no doubt gives the (residuary) estate equally between the 3 beneficiaries and does not require any adjustment be made for variation in a beneficiary’s entitlement depending upon the tax regime to which they are subject (and any such provision could well be unique if included). If an executor needed also to understand the tax consequences for individual beneficiaries when considering a distribution, this could make estates with non-UK beneficiaries almost unmanageable.
I suggest the beneficiaries are advised of the intention to appropriate and sell as bare trustee and, if required, their consent to that appropriation sought. It will then be for the non-UK beneficiary to consider if they should take advice.
If you do not appropriate to the non-UK beneficiary (perhaps because they refuse to consent to the appropriation), when the property is sold the gain on a one-third share will be assessable on the executor, who may, or, may not, haver any CGT allowance available. Any CGT payable will be an administration expense and cannot just be charged to the non-UK beneficiary, who will be entitled to receive a distribution of equivalent value to the property appropriated to their fellow beneficiaries.
In effect, the UK beneficiaries will end up paying two-thirds of any CGT on the non-UK beneficiary’s nominal share of the property, plus two-thirds of the sale costs.
If the property is appropriated to all the beneficiaries, consideration will also need to be given to compliance with the non-UK beneficiary’s duty to submit a CGT computation and pay any CGT due in respect of their share.