and thanks Just Answer.
My name is ***** ***** am happy to assist you with your enquiry.
To make the change legal, so the 2 daughters receive 50% each of the Estate, a codicil has to be drawn up and then executed correctly, (ie it is signed by the person and witnessed by 2 independent people).
A Solicitor does not have to prepare the codicil, so if you are confident that you can draw up a suitable codicil, these chages will become legal on the person's death, provided the codicil is then signed and witnessed as detailed above.
None of the executor(s) or beneficiaries named in the Will need to be notified of the codicil.
I hope this assists and answers your question.
If you require any further clarification, please let me know.