When Will the Courts Consider That a Purported Act of Trustees

When will the courts consider that a purported act of trustees is not void?

A) Where the trust specifies that the terms of the trust may be varied by the trustees executing a deed of variation, and the trustees make a unanimous decision to vary the trust, but fail to use a deed.
B) Where the trustees of a trust to make grants towards the cost of educating the children of employees of a named company give a grant to the child of a cleaner (who is not employed by the company but works through an independent agency) .
C) Where the trustees of a trust to make grants towards the cost of educating the children of employees of a named company have a policy of giving only one grant per child, but in error make a second grant in respect of the same child.
D) Where the trustees make a decision to invest in fine art which they have been (incorrectly) advised by a solicitor is a decision which they can make, but is later discovered to be outside their investment powers.