IHT on residence left to wife and children

Husband has died and has left the PPR 40% to his (second) wife and 60% to his (not her) children. Widow has the right to occupy for life.

It seems that solicitor has said that this is treated as 100% to wife on husband's death and only when the widow dies does the 60% come into charge.

Is this correct? If so, will IHT be payable by husband's estate after widow dies on 2019 value or value a tthe time of widow's death?