Deed of variation

A surviving spouse and her two adult children are looking to enter into a DoV, to vary the intestacy rules and allow the mother to benefit from the entire estate (including interest accrued during the administration).
They wish to submit the DoV together with IHT400 prior to obtaining Grant, to avoid paying IHT.

Can anyone help with the relevant precedent?

Liora Torn-Hibler
Berlad Graham LLP