IHT38 vs Ascertainment of residue

Executors have probate, sufficient assets have been encashed to settle all estate liabilities, admin expenses and pecuniary legacies. HMRC manual CG30810 appears to state that residue has been ascertained by this point.

A few weeks later shares are then sold (approx. 1 year after death), at a gain from the probate value. As per CG30810 it would appear these are sold as bare trustee by the executors and the gain falls on the (multiple) beneficiaries, not the executors.

The deceased’s house is then sold (at over £500k) far lower than probate value, two weeks later. IHT38 loss relief is claimed.

Is the above correct?
How should income tax be dealt with - only up until the date of residue ascertainment by the executors, and then all income/gains are on the beneficiaries? This seems confusing as the sale of a £500k house would prompt the complex estate situation requiring a formal income tax return by the executors.