Mitigating millions

I have an elderly client with a personal estate for inheritance tax purposes valued at £5 million which includes the entire share capital (apart from one share each to her three children) within three private property investment companies valued at £4 million (including approximately £1 million in surplus cash). In addition she is also the life tenant of a trust valued at
£1 million (consisting of property £300 000 and cash £700 000) the capital of which passes to her three children in equal shares on her death. Her own estate similarly passes to her three children in equal shares absolutely.
I would appreciate Taxation readers' opinions as to whether the executors of this estate should upon her death during the administration period and whilst the company shares were still in their names distribute sufficient of the cash within the property companies by...