(a) Unless it is otherwise provided by the trust instrument, or an amendment thereof, or by court order, any power vested in three or more trustees may be exercised by a majority of such trustees; but no trustee who has not joined in exercising a power shall be liable to the beneficiaries or to others for the consequences of such exercise, nor shall a dissenting trustee be liable for the consequences of an act in which he joins at the direction of the majority trustees, if he expressed his dissent in writing to any of his co-trustees at or before the time of such joinder.
(b) Nothing in this section shall excuse a co-trustee from liability for inactivity in the administration of the trust nor for failure to attempt to prevent a breach of trust.