You have not stated that whether the property is in India or in UK.
Assuming the property is in India for which a Will was made in UK.
As Indians increasingly go global whilst retaining assets in India, there is a greater need to understand probate issues in India.
To obtain probate in India, the executors must file a petition with the original Will annexed in the court having jurisdiction in India.
The Will needs to be probated under the applicable law. It is a usual practice to state the law governing the Will especially when it covers assets in different countries. By granting Probate, the competent Court of any jurisdiction gives recognition to authenticity of the Will. Enforcement of foreign probates in India is governed by provisions of Indian Civil Procedure Code and Indian Succession Act, 1925. As a general rule once probate is granted in foreign jurisdiction, Indian Courts will refrain from taking evidence to examine validity of the Will and should grant permission in the form of ancillary probate. This means that Indian court will not entertain any objections to authenticity of the foreign Will.In practice the competent Indian court will grant letter of administration with a copy of the Will attached.
Thus after getting probate of will the will can be executed/enforced by the executor or the beneficiaries.
Your question is:
What we are trying to establish is,does my grandmothers wishes mean the 50% of the property now passes to her daughters or is it now considered part of my fathers estate, becoming part of our inheritance?
You can very well proceed for seeking probate of the will, because your father has not sold the property till his death and thus it becomes his own property, now as legal heirs to your father you can inherit the properties left behind including this property on which he has been bequeathed with a share of 50%.