CLT to trust -IHT consequences

Trusts Discussion
1

If a deceased made a CLT to a trust over NRB and retained a benefit until death could you clarify-

  1. How we address the unpaid CLT charge on death. How do we apportion the tax to trust and the estate as the grob. Trustees and executor are the same individuals.
  2. Can the unpaid tax attributable to the CLT and any penalties be classed as a liability if the estate to reduce any tax payable

Assume as this is governed by RPR there is no spousal exemption on death?

Thank you